splitting an array into two smaller arrays in python

Question

I have an array of size 80x40 and want to send each row into one of two smaller arrays based on a value in a specific column (10). I have code similar to below-but this ends up flattening the array. I don't know the Y dimensions of the output arrays (Array2,Array3). I guess I could have some code count all the values above and below 50 to get the Y dimensions of the output axes and then make 2 output arrays of np.zeros(Array.shape[0],Yvalues) and append row by row to that but I'm still not sure how that would work.

Array.shape=(80,40)
Array2=[]
Array3=[]

for x in range(0,Array.shape[0]):
    if Array[x,10]<50:
        Array2.append(Array[x,:])
    else:
        Array3.append(Array[x,:])

eumiro · Accepted Answer · 2015-02-19 07:32:47Z

1

As a smaller example:

a = np.array([[1, 10], [1, 20], [2, 30], [2, 40], [1, 50], [3, 60], [1, 70]])

a2 = a[a[:, 0] < 1.5]
a3 = a[a[:, 0] >= 1.5]

a2 is now:

array([[ 1, 10],
       [ 1, 20],
       [ 1, 50],
       [ 1, 70]])

and a3 is now:

array([[ 2, 30],
       [ 2, 40],
       [ 3, 60]])

So in your case, use:

a2 = a[a[:, 10] < 50]
a3 = a[a[:, 10] >= 50]

answered Feb 19, 2015 at 7:32

eumiro

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