R Moving-average per group

Question

I got a data.frame ABC_Score.

ABC_Score <- data.frame(Level = c("A", "A", "A", "B", "B", "C", "C", 
"C", "C"), result = c(2, 3, 3, 7, 9, 18, 20, 17, 20))

What I need is the moving average of the result per Level.

Currently I have the moving average with the following script.

install.packages("TTR")
library(TTR)

`ABC_Score$MA` <- runMean(ABC_Score$result, 2)

      Level result   MA
    1     A      2   NA
    2     A      3  2.5
    3     A      3  3.0
    4     B      7  5.0
    5     B      9  8.0
    6     C     18 13.5
    7     C     20 19.0
    8     C     17 18.5
    9     C     20 18.5

but here I need to specify the number of rows (result) where the moving average will be calculated over. In this example 2 which is incorrect since results from different Levels are now mixed in the moving average.

How can the moving average automatically be calculated over the result per Level?

Waist

have you looked at by and zoo::rollmean? – Prefigure

Possible duplicate: #26199051 – Harlequinade

Answer 1

You could use group_by and mutate from dplyr.

library(TTR)
library(dplyr)
ABC_Score <- data.frame(
    Level = c("A", "A", "A", "B", "B", "C", "C", "C", "C"), 
    result = c(2, 3, 3, 7, 9, 18, 20, 17, 20))
ABC_Score %>% group_by(Level) %>% mutate(ra = runMean(result, 2))
# A tibble: 9 x 3
# Groups:   Level [3]
   Level result    ra
  <fctr>  <dbl> <dbl>
1      A      2    NA
2      A      3   2.5
3      A      3   3.0
4      B      7    NA
5      B      9   8.0
6      C     18    NA
7      C     20  19.0
8      C     17  18.5
9      C     20  18.5

Zimmer

What if there was NAs in column result, will it work? – Attaint

The runMean function complains if there are any NA values. – Zimmer

Always use dplyr::mutate to avoid unexpected results. – Lookeron

Answer 2

Using function on sinbgle vectors with levels of a factor is what the ave function does:

 ABC_Score$MA <- with(ABC_Score, ave(result, Level, FUN=function(x) 
                     TTR::runMean(x, n=2)) )
> ABC_Score
  Level result   MA
1     A      2   NA
2     A      3  2.5
3     A      3  3.0
4     B      7   NA
5     B      9  8.0
6     C     18   NA
7     C     20 19.0
8     C     17 18.5
9     C     20 18.5

Frizzly