plotting a row of 3 plots using matplotlib and numpy but getting "IndexError: too many indices for array"

Question

I am trying to plot a panel of 3 plots using matplotlib and the subplots() method. I have a numpy array of the mean values for the data and a second array for the standard error for the mean values. I tried to create a plot but keep getting an IndexError: too many indices for array.

The numpy array looks like this:

mean_matrix

f1    f2    f3
8.3   4.1   12.9
8.5   4.3   11.2

std_matrix

f1    f2    f3
2.3   0.4   1.2
1.2   0.2  1.3

So here is my code. As you can see, I am trying to plot the mean and then use a fill for 1.96 times the standard error.

f, axarr = plt.subplots(nrows = 1, ncols=3)

axarr[0,0].plot(range(duration), mean_matrix['f1'], subplots=True)
axarr[0,0].fill_between(range(duration), mean_matrix['f1'] +
                    1.96*std_matrix['f1'], mean_matrix['f1'] -
                    1.96*std_matrix['f1'], alpha=0.5)

axarr[0,1].plot(range(duration), mean_matrix['f2'], subplots=True)
axarr[0,1].fill_between(range(duration), mean_matrix['f2'] +
                    1.96*std_matrix['f2'], mean_matrix['f2'] -
                    1.96*std_matrix['f2'], alpha=0.5 )

axarr[0,2].plot(range(duration), mean_matrix['f3'], subplots=True)
axarr[0,2].fill_between(range(duration), mean_matrix['f3'] +
                    1.96*std_matrix['f3'], mean_matrix['f3'] -
                    1.96*std_matrix['f3'], alpha=0.5 )

I get the error: IndexError: too many indices for array

@all_m sorry for our colliding answers (and thanks for giving it over), I saw that you were delayed by formatting the question:) I added the extra bit of info from your answer to my own, I hope you don't mind (and please let me know if you do). — Andras Deak -- Слава Україні
– Andras Deak -- Слава Україні, Commented Oct 19, 2015 at 22:50

Community · Accepted Answer · 2017-05-23 12:33:10Z

4

If you issue the subplots command:

f, axarr = plt.subplots(nrows = 1, ncols=3)

You will find that

In [7]: axarr.shape
Out[7]: (3,)

In other words, it is a 1d array. Trying to access it with two indices should give an error:

In [4]: axarr
Out[4]: 
array([<matplotlib.axes._subplots.AxesSubplot object at 0x7f0e299dead0>,
       <matplotlib.axes._subplots.AxesSubplot object at 0x7f0e107d3110>,
       <matplotlib.axes._subplots.AxesSubplot object at 0x7f0e1804d5d0>], dtype=object)

In [5]: axarr[0,0]
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-5-3e75475f2c86> in <module>()
----> 1 axarr[0,0]

IndexError: too many indices

Just try your plot commands with axarr[0] etc.

As @all_m noted, this behaviour is expected if either nrows==1 or ncols==1 in the subplots call, i.e. if you either have a single row or a single column of subplots.

edited May 23, 2017 at 12:33

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answered Oct 19, 2015 at 22:37

Andras Deak -- Слава Україні

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2 Comments

krishnab Over a year ago

Oh that is interesting. So I was messing up the rows and columns. @Andras thanks for that insight.

Andras Deak -- Слава Україні Over a year ago

@krishnab, no, you didn't. As @all_m added in a now-deleted answer, if one of your dimensions is singleton (i.e. you have either just a row or just a column of plots) then the resulting axarr will be 1d.

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