How to add a title to each subplot

Question

I have one figure which contains many subplots.

fig = plt.figure(num=None, figsize=(26, 12), dpi=80, facecolor='w', edgecolor='k')
fig.canvas.set_window_title('Window Title')

# Returns the Axes instance
ax = fig.add_subplot(311) 
ax2 = fig.add_subplot(312) 
ax3 = fig.add_subplot(313) 

How do I add titles to the subplots?

fig.suptitle adds a title to all graphs and although ax.set_title() exists, the latter does not add any title to my subplots.

Thank you for your help.

Edit: Corrected typo about set_title(). Thanks Rutger Kassies

Eligible

Answer 1

ax.title.set_text('My Plot Title') seems to work too.

fig = plt.figure()
ax1 = fig.add_subplot(221)
ax2 = fig.add_subplot(222)
ax3 = fig.add_subplot(223)
ax4 = fig.add_subplot(224)
ax1.title.set_text('First Plot')
ax2.title.set_text('Second Plot')
ax3.title.set_text('Third Plot')
ax4.title.set_text('Fourth Plot')
plt.show()

Hildehildebrand

For anyone having problems with the font size for a histogram, oddly enough reducing the number of bins let me increase it. Went from 500 to 100. – Lakes

If you need to be able to specify the fontsize, use ax.set_title('title', fontsize=16) instead. – Soule

@TobiasP.G., how do you position the title inside the subplot? – Mashburn

Hi @Jarad, thank you for your answer. At that time, I used ax2.text() because ax2.title.set_y() wasn't somehow working. Given 4 subplots of the same size, if I gave a value of $0.9$ for $y$ to each subplot's axis.title.set_y(), it still put the titles at weird locations and didn't match for each subplot. – Mashburn

Answer 2

ax.set_title() should set the titles for separate subplots:

import matplotlib.pyplot as plt


data = [1, 2, 3, 4, 5]

fig = plt.figure()
fig.suptitle("Title for whole figure", fontsize=16)
ax = plt.subplot(2, 1, 1)
ax.set_title("Title for first plot")
ax.plot(data)

ax = plt.subplot(2, 1, 2)
ax.set_title("Title for second plot")
ax.plot(data)

plt.show()

Can you check if this code works for you? Maybe something overwrites them later?

Plod

This works for me, matplotlib version 1.2.2 python 2.7.5 – Churl

On matplotlib 3.5.2 this throws a ValueError on plt.subplot("211") / plt.subplot("212") . The solution is to just replace with integer arguments, plt.subplot(211) & plt.subplot(212). – Physiological

Answer 3

A shorthand answer assuming import matplotlib.pyplot as plt:

plt.gca().set_title('title')

as in:

plt.subplot(221)
plt.gca().set_title('title')
plt.subplot(222)
etc...

Then there is no need for superfluous variables.

Bandwidth

this approach is nice because it gives more control over the title position...e.g. by adding kwarg y=0.7 you can plot the subplot title within the subplot – Kamerad

Answer 4

If you want to make it shorter, you could write :

import matplotlib.pyplot as plt
for i in range(4):
    plt.subplot(2,2,i+1).set_title(f'Subplot n°{i+1}')
plt.show()

It makes it maybe less clear but you don't need more lines or variables

Wharfage

Answer 5

A solution I tend to use more and more is this one:

import matplotlib.pyplot as plt

fig, axs = plt.subplots(2, 2)  # 1
for i, ax in enumerate(axs.ravel()): # 2
    ax.set_title("Plot #{}".format(i)) # 3

1. Create your arbitrary number of axes
2. axs.ravel() converts your 2-dim object to a 1-dim vector in row-major style
3. assigns the title to the current axis-object

Bandwidth

Answer 6

For completeness, the requested result can also be achieve without explicit reference to the figure axes as follows:

import matplotlib.pyplot as plt

plt.subplot(221)
plt.title("Title 1")

plt.subplot(222)
plt.title("Title 2")

plt.subplot(223)
plt.title("Title 3")

plt.subplot(224)
plt.title("Title 4")

Use plt.tight_layout() after the last plot if you have issues with overlapping labels.

Astro

Answer 7

fig, (ax1, ax2, ax3, ax4) = plt.subplots(nrows=1, ncols=4,figsize=(11, 7))

grid = plt.GridSpec(2, 2, wspace=0.2, hspace=0.5)

ax1 = plt.subplot(grid[0, 0])
ax2 = plt.subplot(grid[0, 1:])
ax3 = plt.subplot(grid[1, :1])
ax4 = plt.subplot(grid[1, 1:])

ax1.title.set_text('First Plot')
ax2.title.set_text('Second Plot')
ax3.title.set_text('Third Plot')
ax4.title.set_text('Fourth Plot')

plt.show()

Paediatrician

how to add space between subplots and their titles. – Toothless

Answer 8

In case you have multiple images and you want to loop though them and show them 1 by 1 along with titles - this is what you can do. No need to explicitly define ax1, ax2, etc.

1. The catch is you can define dynamic axes(ax) as in Line 1 of code and you can set its title inside a loop.
2. The rows of 2D array is length (len) of axis(ax)
3. Each row has 2 items i.e. It is list within a list (Point No.2)
4. set_title can be used to set title, once the proper axes(ax) or subplot is selected.

import matplotlib.pyplot as plt    
fig, ax = plt.subplots(2, 2, figsize=(6, 8))  
for i in range(len(ax)): 
    for j in range(len(ax[i])):
        ## ax[i,j].imshow(test_images_gr[0].reshape(28,28))
        ax[i,j].set_title('Title-' + str(i) + str(j))

Utile

Answer 9

You are able to give every graph a different title and label by Iteration only.

titles = {221: 'First Plot', 222: 'Second Plot', 223: 'Third Plot', 224: 'Fourth Plot'}
fig = plt.figure()
for x in range(221,225):
  ax = fig.add_subplot(x)
  ax.title.set_text(titles.get(x))

plt.subplots_adjust(left=0.1,
                    bottom=0.1, 
                    right=0.9, 
                    top=0.9, 
                    wspace=0.4, 
                    hspace=0.4)
plt.show()

Output:

Squiggle

the subplots_adjust call cures overlapping titles. So this is very useful. Thank you! – Flabellate

How to add some space between the subplot's title and its plot. For eg. vertical space between the heading First plot and its corressponding plot – Toothless

Answer 10

As of matplotlib 3.4.3, the Figure.add_subplot function supports kwargs with title as:

fig.add_subplot(311, title="first")
fig.add_subplot(312, title="second")

Marasco

Simple and works perfectly (don't know why this doesn't have more upvotes) – Ferrante