deleting rows in numpy array

Question

I have an array that might look like this   ANOVAInputMatrixValuesArray      0 96488889  0 73641667  0 67521429  0 592875   0 53172222     0 78008333  0 5938125  0 481  0 39883333  0      Notice that one of the rows has a zero value at the end   I want to delete any row that contains a zero  while keeping any row that contains non-zero values in all cells   But the array will have different numbers of rows every time it is populated  and the zeros will be located in different rows each time   I get the number of non-zero elements in each row with the following line of code   NumNonzeroElementsInRows       ANOVAInputMatrixValuesArray    0  sum 1    For the array above  NumNonzeroElementsInRows contains   5 4   The five indicates that all possible values in row 0 are nonzero  while the four indicates that one of the possible values in row 1 is a zero   Therefore  I am trying to use the following lines of code to find and delete rows that contain zero values   for q in range len NumNonzeroElementsInRows        if NumNonzeroElementsInRows q   lt  NumNonzeroElementsInRows max            p delete ANOVAInputMatrixValuesArray  q  axis 0    But for some reason  this code does not seem to do anything  even though doing a lot of print commands indicates that all of the variables seem to be populating correctly leading up to the code   There must be some easy way to simply  delete any row that contains a zero value    Can anyone show me what code to write to accomplish this

User · Answer

The simplest way to delete rows and columns from arrays is the numpy.delete method.

Suppose I have the following array x:

x = array([[1,2,3],
        [4,5,6],
        [7,8,9]])

To delete the first row, do this:

x = numpy.delete(x, (0), axis=0)

To delete the third column, do this:

x = numpy.delete(x,(2), axis=1)

So you could find the indices of the rows which have a 0 in them, put them in a list or a tuple and pass this as the second argument of the function.

User · Answer

numpy provides a simple function to do the exact same thing  supposing you have a masked array  a   calling numpy ma compress rows a  will delete the rows containing a masked value  I guess this is much faster this way

User · Answer

I might be too late to answer this question  but wanted to share my input for the benefit of the community  For this example  let me call your matrix  ANOVA   and I am assuming you re just trying to remove rows from this matrix with 0 s only in the 5th column   indx      for i in range len ANOVA        if int ANOVA i 4      int 0           indx append i   ANOVA    x for x in ANOVA if not x in indx

User · Answer

import numpy as np  arr   np array    0 96488889  0 73641667  0 67521429  0 592875  0 53172222    0 78008333  0 5938125  0 481  0 39883333  0     print arr np where arr    0

User · Answer

Here s a one liner  yes  it is similar to user333700 s  but a little more straightforward     gt  gt  gt  import numpy as np  gt  gt  gt  arr   np array    0 96488889  0 73641667  0 67521429  0 592875  0 53172222                      0 78008333  0 5938125  0 481  0 39883333  0      gt  gt  gt  print arr arr all 1   array    0 96488889   0 73641667   0 67521429   0 592875     0 53172222      By the way  this method is much  much faster than the masked array method for large matrices  For a 2048 x 5 matrix  this method is about 1000x faster   By the way  user333700 s method  from his comment  was slightly faster in my tests  though it boggles my mind why

User · Answer

This is similar to your original approach  and will use less space than unutbu s answer  but I suspect it will be slower    gt  gt  gt  import numpy as np  gt  gt  gt  p   np array   1 5  0    1 4 1 5    1 6  0    1 7  1 8     gt  gt  gt  p array    1 5   0              1 4   1 5            1 6   0              1 7   1 8     gt  gt  gt  nz    p    0  sum 1   gt  gt  gt  q   p nz    0      gt  gt  gt  q array    1 4   1 5            1 7   1 8      By the way  your line p delete   doesn t work for me - ndarrays don t have a  delete attribute

[python] deleting rows in numpy array

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