Selection from JSON

Question

I recently started learning JavaScript and faced a task that I can't complete in any way, every time I get the wrong data that I need There is an object that contains data on banking transactions, I need to make a selection and form a new object using filter, map or reduce:

We assume that the initial balance on the card = 0.

1. Output the TOP 3 months with the largest number of operations by month.

Formalize it as a task_1(arr) function, where arr is the source array with data for all months.

Output format:

[
    { year: 2019, month: 11, opsCount: 27 },
    { year: 2019, month: 10, opsCount: 26 },
    { year: 2019, month: 8, opsCount: 24 }
]

2. Output statistics for the end of the specified month.

• monthmonthBalance - own balance by month = The amount of all deposits minus the amount of all debits
• montWithdrawal – total cash withdrawal amount
• withdrawalRate – the share of the total amount of debits from the total amount of deposits per month.
• rank – user status calculated by the formula:

Gold if withdrawalRate < 0.15.

Silver if withdrawalRate < 0.3.

Bronze in all other cases.

Formalize it as a task_2(year, month, arr) function, where year, month is the desired one month, and arr is the original array with all the data by month.

Output format:

{
date: '2019-01-31’,
monthBalance: 3829,
monthWithrawal: 33800,
withdrawalRate: 0.3133
rank: 'Bronze’
}

3. Calculate statistics from task 2 for all months of the period. Add a field to each month

• totalBalance - cumulative balance = Own balance for the month + Balance for the cumulative balance for the previous month.

Output format:

[
{
date: '2019-01-31’,
monthBalance: 3829,
totalBalance: 3829,
monthWithrawal: 33800,
withdrawalRate: 0.3133
rank: ’Bronze'
},
...
]

Formalize it as a task_3(arr) function, where arr is the source array with data.

JSON with data:

[
    { "year": 2019, "month": 1, "day": 1, "type": "replenishment", "amount": 79817 },
    { "year": 2019, "month": 1, "day": 3, "type": "payment", "amount": 11334 },
    { "year": 2019, "month": 1, "day": 5, "type": "withdrawal", "amount": 26700 },
    { "year": 2019, "month": 1, "day": 5, "type": "payment", "amount": 15475 },
    { "year": 2019, "month": 1, "day": 6, "type": "payment", "amount": 4818 },
    { "year": 2019, "month": 1, "day": 6, "type": "payment", "amount": 1893 },
    { "year": 2019, "month": 1, "day": 7, "type": "payment", "amount": 3844 },
    { "year": 2019, "month": 1, "day": 7, "type": "withdrawal", "amount": 3100 },
    { "year": 2019, "month": 1, "day": 7, "type": "payment", "amount": 3230 },
    { "year": 2019, "month": 1, "day": 7, "type": "payment", "amount": 2427 },
    { "year": 2019, "month": 1, "day": 9, "type": "replenishment", "amount": 15835 },
    { "year": 2019, "month": 1, "day": 10, "type": "payment", "amount": 9670 },
    { "year": 2019, "month": 1, "day": 11, "type": "payment", "amount": 582 },
    { "year": 2019, "month": 1, "day": 11, "type": "withdrawal", "amount": 1100 },
    { "year": 2019, "month": 1, "day": 11, "type": "replenishment", "amount": 5971 },
    { "year": 2019, "month": 1, "day": 12, "type": "payment", "amount": 173 },
    { "year": 2019, "month": 1, "day": 14, "type": "withdrawal", "amount": 1500 },
    { "year": 2019, "month": 1, "day": 14, "type": "payment", "amount": 3641 },
    { "year": 2019, "month": 1, "day": 16, "type": "payment", "amount": 4669 },
    { "year": 2019, "month": 1, "day": 18, "type": "payment", "amount": 2460 },
    { "year": 2019, "month": 1, "day": 19, "type": "payment", "amount": 1307 },
    { "year": 2019, "month": 1, "day": 20, "type": "withdrawal", "amount": 1400 },
    { "year": 2019, "month": 1, "day": 21, "type": "payment", "amount": 952 },
    { "year": 2019, "month": 1, "day": 21, "type": "payment", "amount": 561 },
    { "year": 2019, "month": 1, "day": 21, "type": "replenishment", "amount": 6236 },
    { "year": 2019, "month": 1, "day": 22, "type": "payment", "amount": 888 },
    { "year": 2019, "month": 1, "day": 22, "type": "payment", "amount": 2306 },
    { "year": 2019, "month": 2, "day": 1, "type": "replenishment", "amount": 84839 },
    { "year": 2019, "month": 2, "day": 1, "type": "withdrawal", "amount": 27700 },
    { "year": 2019, "month": 2, "day": 1, "type": "payment", "amount": 11145 },
    { "year": 2019, "month": 2, "day": 2, "type": "payment", "amount": 4075 },
    { "year": 2019, "month": 2, "day": 4, "type": "withdrawal", "amount": 10900 },
    { "year": 2019, "month": 2, "day": 6, "type": "payment", "amount": 10537 },
    { "year": 2019, "month": 2, "day": 6, "type": "payment", "amount": 6001 },
    { "year": 2019, "month": 2, "day": 7, "type": "withdrawal", "amount": 7300 },
    { "year": 2019, "month": 2, "day": 10, "type": "withdrawal", "amount": 1500 },
    { "year": 2019, "month": 2, "day": 10, "type": "payment", "amount": 3584 },
    { "year": 2019, "month": 2, "day": 11, "type": "payment", "amount": 701 },
    { "year": 2019, "month": 3, "day": 1, "type": "replenishment", "amount": 84771 },
    { "year": 2019, "month": 3, "day": 3, "type": "withdrawal", "amount": 22700 },
    { "year": 2019, "month": 3, "day": 5, "type": "payment", "amount": 12352 },
    { "year": 2019, "month": 3, "day": 8, "type": "payment", "amount": 2795 },
    { "year": 2019, "month": 3, "day": 11, "type": "withdrawal", "amount": 16600 },
    { "year": 2019, "month": 3, "day": 11, "type": "replenishment", "amount": 4141 },
    { "year": 2019, "month": 3, "day": 11, "type": "payment", "amount": 9854 },
    { "year": 2019, "month": 3, "day": 13, "type": "withdrawal", "amount": 1200 },
    { "year": 2019, "month": 3, "day": 14, "type": "payment", "amount": 11573 },
    { "year": 2019, "month": 3, "day": 14, "type": "payment", "amount": 5138 },
    { "year": 2019, "month": 3, "day": 15, "type": "payment", "amount": 731 },
    { "year": 2019, "month": 3, "day": 17, "type": "payment", "amount": 5053 },
    { "year": 2019, "month": 3, "day": 19, "type": "withdrawal", "amount": 400 },
    { "year": 2019, "month": 3, "day": 20, "type": "payment", "amount": 1745 },
    { "year": 2019, "month": 3, "day": 20, "type": "payment", "amount": 602 },
    { "year": 2019, "month": 3, "day": 21, "type": "payment", "amount": 178 },
    { "year": 2019, "month": 3, "day": 22, "type": "payment", "amount": 353 },
    { "year": 2019, "month": 3, "day": 23, "type": "payment", "amount": 837 },
    { "year": 2019, "month": 3, "day": 23, "type": "payment", "amount": 330 },
    { "year": 2019, "month": 3, "day": 23, "type": "payment", "amount": 799 },
    { "year": 2019, "month": 3, "day": 24, "type": "payment", "amount": 294 },
    { "year": 2019, "month": 3, "day": 24, "type": "payment", "amount": 260 },
    { "year": 2019, "month": 3, "day": 25, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 4, "day": 1, "type": "replenishment", "amount": 88656 },
    { "year": 2019, "month": 4, "day": 4, "type": "payment", "amount": 37852 },
    { "year": 2019, "month": 4, "day": 7, "type": "payment", "amount": 9365 },
    { "year": 2019, "month": 4, "day": 8, "type": "payment", "amount": 16701 },
    { "year": 2019, "month": 4, "day": 11, "type": "payment", "amount": 8979 },
    { "year": 2019, "month": 4, "day": 11, "type": "payment", "amount": 1971 },
    { "year": 2019, "month": 4, "day": 13, "type": "payment", "amount": 1261 },
    { "year": 2019, "month": 4, "day": 13, "type": "withdrawal", "amount": 800 },
    { "year": 2019, "month": 4, "day": 15, "type": "payment", "amount": 5553 },
    { "year": 2019, "month": 4, "day": 17, "type": "payment", "amount": 2593 },
    { "year": 2019, "month": 4, "day": 18, "type": "replenishment", "amount": 6915 },
    { "year": 2019, "month": 4, "day": 19, "type": "replenishment", "amount": 17647 },
    { "year": 2019, "month": 4, "day": 21, "type": "payment", "amount": 13814 },
    { "year": 2019, "month": 4, "day": 22, "type": "payment", "amount": 2707 },
    { "year": 2019, "month": 4, "day": 22, "type": "withdrawal", "amount": 1300 },
    { "year": 2019, "month": 4, "day": 22, "type": "withdrawal", "amount": 2900 },
    { "year": 2019, "month": 4, "day": 23, "type": "replenishment", "amount": 10709 },
    { "year": 2019, "month": 4, "day": 23, "type": "payment", "amount": 686 },
    { "year": 2019, "month": 4, "day": 23, "type": "withdrawal", "amount": 5100 },
    { "year": 2019, "month": 4, "day": 23, "type": "payment", "amount": 3830 },
    { "year": 2019, "month": 5, "day": 1, "type": "replenishment", "amount": 59877 },
    { "year": 2019, "month": 5, "day": 2, "type": "payment", "amount": 14095 },
    { "year": 2019, "month": 5, "day": 5, "type": "payment", "amount": 10858 },
    { "year": 2019, "month": 5, "day": 8, "type": "payment", "amount": 9412 },
    { "year": 2019, "month": 5, "day": 11, "type": "replenishment", "amount": 6892 },
    { "year": 2019, "month": 5, "day": 11, "type": "payment", "amount": 17541 },
    { "year": 2019, "month": 5, "day": 11, "type": "payment", "amount": 2666 },
    { "year": 2019, "month": 5, "day": 11, "type": "payment", "amount": 3935 },
    { "year": 2019, "month": 5, "day": 12, "type": "withdrawal", "amount": 2600 },
    { "year": 2019, "month": 5, "day": 14, "type": "payment", "amount": 2096 },
    { "year": 2019, "month": 5, "day": 14, "type": "replenishment", "amount": 2733 },
    { "year": 2019, "month": 5, "day": 15, "type": "replenishment", "amount": 538 },
    { "year": 2019, "month": 5, "day": 15, "type": "payment", "amount": 5324 },
    { "year": 2019, "month": 5, "day": 15, "type": "payment", "amount": 2490 },
    { "year": 2019, "month": 5, "day": 15, "type": "payment", "amount": 3510 },
    { "year": 2019, "month": 5, "day": 17, "type": "withdrawal", "amount": 300 },
    { "year": 2019, "month": 5, "day": 17, "type": "payment", "amount": 133 },
    { "year": 2019, "month": 6, "day": 1, "type": "replenishment", "amount": 89064 },
    { "year": 2019, "month": 6, "day": 2, "type": "payment", "amount": 7613 },
    { "year": 2019, "month": 6, "day": 2, "type": "payment", "amount": 33742 },
    { "year": 2019, "month": 6, "day": 5, "type": "withdrawal", "amount": 7200 },
    { "year": 2019, "month": 6, "day": 6, "type": "payment", "amount": 15125 },
    { "year": 2019, "month": 6, "day": 9, "type": "payment", "amount": 3379 },
    { "year": 2019, "month": 6, "day": 10, "type": "payment", "amount": 1260 },
    { "year": 2019, "month": 6, "day": 12, "type": "payment", "amount": 11066 },
    { "year": 2019, "month": 6, "day": 12, "type": "replenishment", "amount": 7050 },
    { "year": 2019, "month": 6, "day": 12, "type": "payment", "amount": 7531 },
    { "year": 2019, "month": 6, "day": 13, "type": "payment", "amount": 4776 },
    { "year": 2019, "month": 6, "day": 13, "type": "replenishment", "amount": 4456 },
    { "year": 2019, "month": 6, "day": 14, "type": "replenishment", "amount": 7998 },
    { "year": 2019, "month": 6, "day": 16, "type": "payment", "amount": 2437 },
    { "year": 2019, "month": 6, "day": 16, "type": "replenishment", "amount": 11729 },
    { "year": 2019, "month": 6, "day": 18, "type": "payment", "amount": 11216 },
    { "year": 2019, "month": 6, "day": 19, "type": "payment", "amount": 3420 },
    { "year": 2019, "month": 6, "day": 19, "type": "payment", "amount": 1339 },
    { "year": 2019, "month": 6, "day": 20, "type": "payment", "amount": 5578 },
    { "year": 2019, "month": 6, "day": 21, "type": "withdrawal", "amount": 1600 },
    { "year": 2019, "month": 6, "day": 21, "type": "withdrawal", "amount": 400 },
    { "year": 2019, "month": 7, "day": 1, "type": "replenishment", "amount": 51749 },
    { "year": 2019, "month": 7, "day": 2, "type": "payment", "amount": 2875 },
    { "year": 2019, "month": 7, "day": 2, "type": "payment", "amount": 10315 },
    { "year": 2019, "month": 7, "day": 5, "type": "payment", "amount": 18501 },
    { "year": 2019, "month": 7, "day": 5, "type": "payment", "amount": 12728 },
    { "year": 2019, "month": 7, "day": 7, "type": "payment", "amount": 4505 },
    { "year": 2019, "month": 7, "day": 8, "type": "payment", "amount": 2758 },
    { "year": 2019, "month": 7, "day": 8, "type": "payment", "amount": 60 },
    { "year": 2019, "month": 7, "day": 10, "type": "withdrawal", "amount": 1100 },
    { "year": 2019, "month": 7, "day": 12, "type": "withdrawal", "amount": 1000 },
    { "year": 2019, "month": 7, "day": 13, "type": "payment", "amount": 151 },
    { "year": 2019, "month": 8, "day": 1, "type": "replenishment", "amount": 85156 },
    { "year": 2019, "month": 8, "day": 1, "type": "payment", "amount": 33978 },
    { "year": 2019, "month": 8, "day": 2, "type": "payment", "amount": 6548 },
    { "year": 2019, "month": 8, "day": 3, "type": "payment", "amount": 5909 },
    { "year": 2019, "month": 8, "day": 6, "type": "payment", "amount": 2326 },
    { "year": 2019, "month": 8, "day": 6, "type": "payment", "amount": 17798 },
    { "year": 2019, "month": 8, "day": 9, "type": "replenishment", "amount": 10770 },
    { "year": 2019, "month": 8, "day": 10, "type": "withdrawal", "amount": 7400 },
    { "year": 2019, "month": 8, "day": 12, "type": "payment", "amount": 6065 },
    { "year": 2019, "month": 8, "day": 14, "type": "withdrawal", "amount": 900 },
    { "year": 2019, "month": 8, "day": 14, "type": "withdrawal", "amount": 1400 },
    { "year": 2019, "month": 8, "day": 14, "type": "payment", "amount": 4673 },
    { "year": 2019, "month": 8, "day": 15, "type": "payment", "amount": 960 },
    { "year": 2019, "month": 8, "day": 15, "type": "payment", "amount": 1085 },
    { "year": 2019, "month": 8, "day": 17, "type": "payment", "amount": 3723 },
    { "year": 2019, "month": 8, "day": 17, "type": "payment", "amount": 2522 },
    { "year": 2019, "month": 8, "day": 19, "type": "replenishment", "amount": 2496 },
    { "year": 2019, "month": 8, "day": 20, "type": "payment", "amount": 876 },
    { "year": 2019, "month": 8, "day": 20, "type": "payment", "amount": 2504 },
    { "year": 2019, "month": 8, "day": 21, "type": "payment", "amount": 826 },
    { "year": 2019, "month": 8, "day": 22, "type": "payment", "amount": 768 },
    { "year": 2019, "month": 8, "day": 23, "type": "withdrawal", "amount": 700 },
    { "year": 2019, "month": 8, "day": 23, "type": "payment", "amount": 190 },
    { "year": 2019, "month": 8, "day": 24, "type": "payment", "amount": 235 },
    { "year": 2019, "month": 9, "day": 1, "type": "replenishment", "amount": 95512 },
    { "year": 2019, "month": 9, "day": 3, "type": "payment", "amount": 26758 },
    { "year": 2019, "month": 9, "day": 3, "type": "replenishment", "amount": 8377 },
    { "year": 2019, "month": 9, "day": 4, "type": "payment", "amount": 30865 },
    { "year": 2019, "month": 9, "day": 4, "type": "withdrawal", "amount": 12800 },
    { "year": 2019, "month": 9, "day": 7, "type": "payment", "amount": 10518 },
    { "year": 2019, "month": 9, "day": 8, "type": "payment", "amount": 11007 },
    { "year": 2019, "month": 9, "day": 10, "type": "payment", "amount": 5613 },
    { "year": 2019, "month": 9, "day": 10, "type": "withdrawal", "amount": 1700 },
    { "year": 2019, "month": 9, "day": 12, "type": "payment", "amount": 2237 },
    { "year": 2019, "month": 9, "day": 14, "type": "payment", "amount": 885 },
    { "year": 2019, "month": 9, "day": 14, "type": "payment", "amount": 977 },
    { "year": 2019, "month": 9, "day": 15, "type": "payment", "amount": 766 },
    { "year": 2019, "month": 9, "day": 17, "type": "payment", "amount": 360 },
    { "year": 2019, "month": 9, "day": 18, "type": "payment", "amount": 116 },
    { "year": 2019, "month": 9, "day": 18, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 9, "day": 19, "type": "payment", "amount": 115 },
    { "year": 2019, "month": 9, "day": 20, "type": "payment", "amount": 50 },
    { "year": 2019, "month": 9, "day": 21, "type": "payment", "amount": 32 },
    { "year": 2019, "month": 10, "day": 1, "type": "replenishment", "amount": 90475 },
    { "year": 2019, "month": 10, "day": 1, "type": "replenishment", "amount": 8845 },
    { "year": 2019, "month": 10, "day": 2, "type": "payment", "amount": 7121 },
    { "year": 2019, "month": 10, "day": 3, "type": "payment", "amount": 27955 },
    { "year": 2019, "month": 10, "day": 3, "type": "payment", "amount": 23079 },
    { "year": 2019, "month": 10, "day": 4, "type": "payment", "amount": 5948 },
    { "year": 2019, "month": 10, "day": 7, "type": "withdrawal", "amount": 4400 },
    { "year": 2019, "month": 10, "day": 8, "type": "payment", "amount": 9677 },
    { "year": 2019, "month": 10, "day": 9, "type": "payment", "amount": 3912 },
    { "year": 2019, "month": 10, "day": 9, "type": "replenishment", "amount": 3870 },
    { "year": 2019, "month": 10, "day": 9, "type": "payment", "amount": 6949 },
    { "year": 2019, "month": 10, "day": 10, "type": "withdrawal", "amount": 3400 },
    { "year": 2019, "month": 10, "day": 10, "type": "replenishment", "amount": 7471 },
    { "year": 2019, "month": 10, "day": 10, "type": "payment", "amount": 5962 },
    { "year": 2019, "month": 10, "day": 10, "type": "payment", "amount": 4990 },
    { "year": 2019, "month": 10, "day": 10, "type": "withdrawal", "amount": 3000 },
    { "year": 2019, "month": 10, "day": 11, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 10, "day": 12, "type": "withdrawal", "amount": 1300 },
    { "year": 2019, "month": 10, "day": 13, "type": "payment", "amount": 986 },
    { "year": 2019, "month": 10, "day": 14, "type": "replenishment", "amount": 4225 },
    { "year": 2019, "month": 10, "day": 15, "type": "withdrawal", "amount": 900 },
    { "year": 2019, "month": 10, "day": 17, "type": "payment", "amount": 864 },
    { "year": 2019, "month": 10, "day": 17, "type": "withdrawal", "amount": 1000 },
    { "year": 2019, "month": 10, "day": 18, "type": "payment", "amount": 801 },
    { "year": 2019, "month": 10, "day": 19, "type": "withdrawal", "amount": 300 },
    { "year": 2019, "month": 10, "day": 20, "type": "payment", "amount": 530 },
    { "year": 2019, "month": 11, "day": 1, "type": "replenishment", "amount": 80285 },
    { "year": 2019, "month": 11, "day": 3, "type": "payment", "amount": 38155 },
    { "year": 2019, "month": 11, "day": 6, "type": "payment", "amount": 10260 },
    { "year": 2019, "month": 11, "day": 9, "type": "payment", "amount": 11013 },
    { "year": 2019, "month": 11, "day": 10, "type": "payment", "amount": 1232 },
    { "year": 2019, "month": 11, "day": 12, "type": "withdrawal", "amount": 5100 },
    { "year": 2019, "month": 11, "day": 12, "type": "payment", "amount": 1192 },
    { "year": 2019, "month": 11, "day": 13, "type": "withdrawal", "amount": 4500 },
    { "year": 2019, "month": 11, "day": 14, "type": "replenishment", "amount": 4304 },
    { "year": 2019, "month": 11, "day": 15, "type": "withdrawal", "amount": 700 },
    { "year": 2019, "month": 11, "day": 15, "type": "replenishment", "amount": 15857 },
    { "year": 2019, "month": 11, "day": 17, "type": "payment", "amount": 9134 },
    { "year": 2019, "month": 11, "day": 19, "type": "payment", "amount": 8090 },
    { "year": 2019, "month": 11, "day": 20, "type": "payment", "amount": 2117 },
    { "year": 2019, "month": 11, "day": 20, "type": "withdrawal", "amount": 2700 },
    { "year": 2019, "month": 11, "day": 21, "type": "withdrawal", "amount": 2200 },
    { "year": 2019, "month": 11, "day": 21, "type": "payment", "amount": 258 },
    { "year": 2019, "month": 11, "day": 21, "type": "withdrawal", "amount": 1200 },
    { "year": 2019, "month": 11, "day": 21, "type": "payment", "amount": 1966 },
    { "year": 2019, "month": 11, "day": 21, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 11, "day": 21, "type": "payment", "amount": 493 },
    { "year": 2019, "month": 11, "day": 21, "type": "payment", "amount": 396 },
    { "year": 2019, "month": 11, "day": 21, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 11, "day": 21, "type": "payment", "amount": 134 },
    { "year": 2019, "month": 11, "day": 22, "type": "replenishment", "amount": 4815 },
    { "year": 2019, "month": 11, "day": 22, "type": "withdrawal", "amount": 500 },
    { "year": 2019, "month": 11, "day": 23, "type": "payment", "amount": 1793 },
    { "year": 2019, "month": 12, "day": 1, "type": "replenishment", "amount": 93524 },
    { "year": 2019, "month": 12, "day": 2, "type": "payment", "amount": 44289 },
    { "year": 2019, "month": 12, "day": 2, "type": "payment", "amount": 7724 },
    { "year": 2019, "month": 12, "day": 4, "type": "payment", "amount": 9420 },
    { "year": 2019, "month": 12, "day": 4, "type": "withdrawal", "amount": 3200 },
    { "year": 2019, "month": 12, "day": 4, "type": "payment", "amount": 651 },
    { "year": 2019, "month": 12, "day": 6, "type": "payment", "amount": 9259 },
    { "year": 2019, "month": 12, "day": 6, "type": "withdrawal", "amount": 5700 },
    { "year": 2019, "month": 12, "day": 7, "type": "payment", "amount": 1298 },
    { "year": 2019, "month": 12, "day": 9, "type": "payment", "amount": 3108 },
    { "year": 2019, "month": 12, "day": 11, "type": "withdrawal", "amount": 4300 },
    { "year": 2019, "month": 12, "day": 13, "type": "withdrawal", "amount": 200 },
    { "year": 2019, "month": 12, "day": 13, "type": "replenishment", "amount": 9096 },
    { "year": 2019, "month": 12, "day": 14, "type": "payment", "amount": 7205 },
    { "year": 2019, "month": 12, "day": 16, "type": "payment", "amount": 658 },
    { "year": 2019, "month": 12, "day": 17, "type": "replenishment", "amount": 9654 }
]

First, for the task_1, I get an object that contains values by the key "month":

var arr1 = ops.map(function(item){

return item.month

})

Then I find the sum of the unique values in the resulting array:

quantity var = {};
for (var i = 0; i <arr1.length; i++){
quantity [arr1[i]] = 1 + (quantity [arr1[i]]|/ 0);
}

and I get the counts object in the following form:

counts
{1: 27, 2: 11, 3: 23, 4: 20, 5: 17, 6: 21, 7: 11, 8: 24, 9: 19, 10: 26, 11: 27, 12: 16}

After that, I sort to find the 3 maximum values:

function findMax 3(obj){
var res = [-1,-1,-1];

for (let key in obj){
res[3] = obj[key];
res.sort(function(a,b){return b-a});
}
res.pop();
return res;
}


console.log(findMax3(counts));

In the console I get the following:

[27, 27, 26]

but at the same time, I no longer know the index of the months to which these values relate

Thank you for your answers!

Fearsome

Do you have any limitation about using third part libraryies e.q. lodash? – Pfeffer

I can use only filter, map or reduce – Fearsome

What about .sort .slice operators, are they acceptable? – Pfeffer

Yes, all standard methods – Fearsome

Answer 1

To solve these problems here is the hint "GroupBy using reduce"

As for task1

function task_1(arr) {
    // Dictionary of Month to Object.
    const groupedByMonth = arr.reduce(function (acc, currentValue) {
        let groupKey = currentValue.month;
        if (!acc[groupKey]) {
            acc[groupKey] = {
                year: currentValue.year,
                month: currentValue.month,
                opsCount: 0
            };
        }
        acc[groupKey].opsCount += 1; // ++
        return acc;
    }, {});

    // Sort by opsCount
    function opsSort(a, b) { return b.opsCount - a.opsCount };

    return Object
        .values(groupedByMonth) // Array of Values
        .sort(opsSort)
        .slice(0, 3) // Top 3
}

Once you understand how task 1 is solved, task 2 becomes a bit simpler

Solution for Task 2

function getEndOfMonth(year, month) {
    const date = new Date(year, month, 0);
    let monthStr = "";
    if (month < 10) {
        monthStr += "0";
    }
    monthStr += month;

    return year + "-" + monthStr + "-" + date.getDate();
}

function getRank(rate) {
    if (rate < 0.15)
        return 'Gold';
    if (rate < 0.3)
        return 'Gold';
    return 'Bronze';
}


function task_2(arr) {
    const groupedByMonth = arr.reduce(function (acc, currentValue) {
        let groupKey = currentValue.month;
        if (!acc[groupKey]) {
            acc[groupKey] = {
                date: getEndOfMonth(currentValue.year, currentValue.month),
                monthWithrawal: 0,
                totalDebits: 0,
                totalDeposits: 0
            };
        }

        // Based on type calculate value.
        if (currentValue.type === "replenishment") {
            acc[groupKey].totalDeposits += currentValue.amount;
        } else if (currentValue.type === "payment") {
            acc[groupKey].totalDebits += currentValue.amount;
        } else if (currentValue.type === "withdrawal") {
            acc[groupKey].monthWithrawal += currentValue.amount;
        }

        return acc;
    }, {});

    return Object
        .values(groupedByMonth) // Array of Values
        .map(function (ele) {
            const withdrawalRate = ele.monthWithrawal / ele.totalDeposits;
            return {
                date: ele.date,
                monthBalance: ele.totalDeposits - ele.totalDebits - ele.monthWithrawal,
                monthWithrawal: ele.monthWithrawal,
                withdrawalRate,
                rank: getRank(withdrawalRate)
            };
        });
}

if you have solved task 2, task 3 is just adding reduce/map to task2's solution.

function task_3(arr) {
    // Assuming that task_2 function is defined.
    const task2 = task_2(arr);

    // Can be Solved using reduce.
    return task2
        .map(function (currentValue, index, array) {
            const tmp = currentValue;
            tmp.totalBalance = tmp.monthBalance;
            if (index > 0) { // Not the first element.
                tmp.totalBalance += array[index - 1].totalBalance;
            }
            return tmp;
        })
}

Fount

Answer 2

Task 1

const task_1 = (arr, top = 3) => {
  const ops = arr.reduce((acc, {year,  month}) => {
     const accByMonth = acc.find((obj) => (obj.month === month));
      if (accByMonth) {
          accByMonth.opsCount +=1;
      } else {
         acc.push({ year, month, opsCount: 1 })
      }
      return acc;
   }, []);
        
   const sortedOps = ops.sort(
      (obj1, obj2) => (obj2.opsCount - obj1.opsCount)
   );
   return sortedOps.slice(0, top);
}
        
console.log(task_1(data)); 
//[
//  { year: 2019, month: 1, opsCount: 27 },
//  { year: 2019, month: 11, opsCount: 27 },
//  { year: 2019, month: 10, opsCount: 26 }
//]

Task 2

const getTotalByType = (arr, type) => arr
  .filter((obj) => obj.type === type)
  .reduce((sum, { amount }) => sum + amount, 0);

const getRank = (ratio) =>{
  const ranks = [[0.15, 'Gold'], [0.3, 'Silver'], [Infinity, 'Bronze']]
  return ranks.find(([ rankRatio ]) => ratio < rankRatio)[1];
}

const task_2 = (year, month, arr) => {
  const filteredData = arr.filter((obj) => (obj.year === year) && (obj.month === month));
  const maxDay = Math.max(...filteredData.map(({ day }) => day));
  const date = new Date(year, month - 1, maxDay).toISOString().split('T')[0];
  const monthReplenishment = getTotalByType(filteredData, 'replenishment');
  const monthPayment = getTotalByType(filteredData, 'payment');
  const monthWithdrawal = getTotalByType(filteredData, 'withdrawal');
  const monthBalance = monthReplenishment - monthPayment - monthWithdrawal;
  const withdrawalRate = parseFloat((monthWithdrawal / monthReplenishment).toFixed(4));
  const rank = getRank(withdrawalRate);

  return {
    date,
    monthBalance,
    monthWithdrawal,
    withdrawalRate,
    rank, 
  }
};

console.log(task_2(2019, 7, data));
//{
//  date: '2019-07-13',
//  monthBalance: -2244,
//  monthWithdrawal: 2100,
//  withdrawalRate: 0.0406,
//  rank: 'Gold'
//}

Task 3

const getPeriods = (arr) => arr.
  reduce((acc, {year,  month}) => {
    const isPeriodInAcc = acc.some(
      (obj) => (obj.month === month) && (obj.year === year)
    );
    if (!isPeriodInAcc) {
      acc.push({ year, month })
    }
    return acc;
  }, [])

const task_3 = (arr, initialBalance = 0) => {
  const periods = getPeriods(arr);
  let totalBalance = initialBalance;

  return periods.map(({ year, month }) => {
    const opsByPeriod = task_2(year, month, arr);
    totalBalance += opsByPeriod.monthBalance;
    return {...opsByPeriod, totalBalance}
  });
}
    
    console.log(task_3(data));
//[
//  {
//    date: '2019-01-22',
//    monthBalance: 3829,
//    monthWithdrawal: 33800,
//    withdrawalRate: 0.3134,
//    rank: 'Bronze',
//    totalBalance: 3829
//  },
//  ...
//  {...},
//]

Pfeffer

Yeah, it works. Thank you! Now I'm going to figure out how it works)) – Fearsome

@Fearsome Pay attention that my output is not as in the task, january has aslo 27 operations like november. So, top 3 is different. – Pfeffer

Yeah, i noticed it. I think this is just an example of the structure of an object that should turn out. Anyway, this is better than what I had – Fearsome

@Fearsome Added solution for task 2 and 3. – Pfeffer