Indexing values in a 2D array in python

Question

This shouldn't be that hard. Assume I have a 2D array:

a = [['1' 'George']
     ['5' ' ']
     ['7' 'Jose']
     ['5' ' ']
     ['7','Fred']]

I wish to find all the indexed values where a[:,1] == ' '

My best guess is:

missing_vals = a[a[:,' ']==' '
a[missing_vals]

I don't want the answer:

   ['5','5']

but the answer:

[1,4]

Meaning the 2nd and 5th elements of the array.

Thanks.

Ray Toal · Accepted Answer · 2017-05-29 16:05:50Z

1

This is what you are looking for:

>>> a = [['1', 'George'],
...       ['5', ' '],
...       ['7', 'Jose'],
...       ['5', ' '],
...       ['7','Fred']]
>>> [i for i, [k,v] in enumerate(a) if v == ' ']
[1, 3]

Explanation:

We are asking for all indexes i in list a at which the element [k,v] in a has the element v equal to a space.

edited May 29, 2017 at 16:05

answered May 28, 2017 at 0:31

Ray Toal

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2 Comments

Leigh Over a year ago

I am sorry. I did not specify. What I seek is the position of these in the array? I am not looking for the answer ['5','5'] but this answer: [1,4] . Meaning that if the array starts at 0, the positions for which the second column a == ' '.

Ray Toal Over a year ago

No worries! I rewrote the answer for you.

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