Take average of columns in a numpy array

Question

I have taken data from a csv file using numpy. numpy array has dimensions : 100*20. How do i take average of columns (say col 3,5,8) and replace them with a new column containing average of these 3 cols

If

   col3 = 1,2,3,4
   col5 = 2,3,4,8
   col8 = 3,4,5,6

then I want to remove these 3 columns and insert a new column in which each entry contains an average of values in these 3 columns

I want to insert a new column: 2,3,4,6, delete previous 3 cols and dimension of final array to be 100*28

Is there any numpy function to do this ?

Things that are unclear - 1) How did we end up with 28 cols? 2) What's the reference of "previous" in delete previous 3 cols? 3) Insert the new column where? — Divakar
– Divakar, Commented Aug 29, 2017 at 21:14
i had 30 cols earlier, i take average of col3,5,8 and store them and remove these 3, so cols now are 27. now insert the col where average is taken. so total cols = 28 — Taylor
– Taylor, Commented Aug 29, 2017 at 21:39

Eric Leschinski · Accepted Answer · 2019-02-14 19:31:42Z

4

a = np.arange(100*30).reshape(100,30) # change this to your own data
cols = [2, 4, 7]                      # columns to calculate averages, i.e. 3,5,8
b = a[:, cols]                        # data of the cols
c = b.mean(axis=1)                    # average
a_no_b = np.delete(a, cols, axis=1)   # data without the cols
a_final = np.c_[a_no_b, c]            # final result

edited Feb 14, 2019 at 19:31

Eric Leschinski

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answered Aug 29, 2017 at 22:38

azalea

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Comments

Jakub Bielan · Accepted Answer · 2018-10-31 19:52:22Z

2

For columns axis = 0, so:

X = np.random.randint(0,101,shape=(100,50))
columns_average = X.mean(axis=0)

You get 1D array 'columns_average' with mean for every column, so 50 values.

answered Oct 31, 2018 at 19:52

Jakub Bielan

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1 Comment

Giora Simchoni Over a year ago

(1) the OP has requested average for specific columns (2) with axis=0 you'll get average across rows, not columns

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