Using numpy to select rows based on a condition of one column

Question

I have a file with various columns. Say

1 2 3 4 5 6

2 4 5 6 7 4

3 4 5 6 7 6

2 0 1 5 6 0

2 4 6 8 9 9

I would like to select and save out rows (in each column) in a new file which have the values in column two in the range [0 - 2].

The answer in the new file should be

1 2 3 4 5 6

2 0 1 5 6 0

Kindly assist me. I prefer doing this with numpy in python.

can you show us some code that you have so far? ideally so that we can copy the code run it on our computer and make some changes to make it work? — el_oso
– el_oso, Commented Apr 30, 2021 at 12:24

GoodDeeds · Accepted Answer · 2021-04-30 12:26:23Z

2

For array a, you can use:

a[(a[:,1] <= 2) & (a[:,1] >= 0)]

Here, the condition filters the values in your second column.

For your example:

>>> a
array([[1, 2, 3, 4, 5, 6],
       [2, 4, 5, 6, 7, 4],
       [3, 4, 5, 6, 7, 6],
       [2, 0, 1, 5, 6, 0],
       [2, 4, 6, 8, 9, 9]])
>>> a[(a[:,1] <= 2) & (a[:,1] >= 0)]
array([[1, 2, 3, 4, 5, 6],
       [2, 0, 1, 5, 6, 0]])

answered Apr 30, 2021 at 12:26

GoodDeeds

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