Access elements from nested array in python

Question

Assume I have the following array

test=np.asarray([
    [[ 0.26139668,  0.271985  ,  0.89647514,  0.10352486],
    [ 0.30488212,  0.31384717,  0.84089744,  0.15910256],
    [ 0.32112577,  0.32958562,  0.79216727,  0.20783273]],
    [[ 0.6017121 ,  0.60530397,  0.49432092,  0.50567908],
    [ 0.61610247,  0.61954059,  0.49649699,  0.50350301],
    [ 0.63149809,  0.63477652,  0.49945702,  0.50054298]],
    [[ 0.6017121 ,  0.60530397,  0.49432092,  0.50567908],
    [ 0.61610247,  0.61954059,  0.49649699,  0.50350301],
    [ 0.63149809,  0.63477652,  0.49945702,  0.50054298]],
    [[ 0.6017121 ,  0.60530397,  0.49432092,  0.50567908],
    [ 0.61610247,  0.61954059,  0.49649699,  0.50350301],
    [ 0.63149809,  0.63477652,  0.49945702,  0.50054298]]])

Now the result I am looking for are in the first column of each element from test. So basically I need test[0][:,0] and test[1][:,0] ... and finally test[3][:,0].

I am sure this can be done without a for loop, or not?

Since notation [:] should mean all elements from beginning till end I even tried test[:][:,0]. That didn't work. test[:,0][:,0] wasn't any better either.

So, what would be the alternative to a for loop?

The result should be:

    [0.26139668, 0.30488212, 0.32112577, 0.6017121, 0.61610247, 0.63149809,
 0.6017121, 0.61610247, 0.63149809,0.6017121, 0.61610247, 0.63149809]

Or anything similar to that. (I only need those numbers from the whole array).

show how should look the final result

RomanPerekhrest
– RomanPerekhrest

2017-03-28 19:15:39 +00:00
Commented Mar 28, 2017 at 19:15 — RomanPerekhrest
– RomanPerekhrest, Commented Mar 28, 2017 at 19:15
@RomanPerekhrest OP edited

skrat
– skrat

2017-03-28 19:18:47 +00:00
Commented Mar 28, 2017 at 19:18 — skrat
– skrat, Commented Mar 28, 2017 at 19:18

Kasravnd · Accepted Answer · 2017-03-28 19:25:41Z

7

You have a 3D array so just pass the 0 to the third axis:

In [9]: test[:, :, 0]
Out[9]: 
array([[ 0.26139668,  0.30488212,  0.32112577],
       [ 0.6017121 ,  0.61610247,  0.63149809],
       [ 0.6017121 ,  0.61610247,  0.63149809],
       [ 0.6017121 ,  0.61610247,  0.63149809]])

If you want them all in one array you can just ravel the slice:

In [11]: test[:, :, 0].ravel()
Out[11]: 
array([ 0.26139668,  0.30488212,  0.32112577,  0.6017121 ,  0.61610247,
        0.63149809,  0.6017121 ,  0.61610247,  0.63149809,  0.6017121 ,
        0.61610247,  0.63149809])

edited Mar 28, 2017 at 19:25

answered Mar 28, 2017 at 19:20

Kasravnd

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