[Numpy-discussion] Slice nested arrays, How to

Bob bobmerhebi at gmail.com
Mon Jul 24 10:37:40 EDT 2017


Hello,

I created the following array by converting it from a nested list:

    a = np.array([np.array([ 17.56578416,  16.82712825,  16.57992292, 
15.83534836]),
       np.array([ 17.9002445 ,  17.35024876,  16.69733472,  15.78809856]),
       np.array([ 17.90086839,  17.64315136,  17.40653009,  17.26346787,
        16.99901931,  16.87787178,  16.68278558,  16.56006419, 
16.43672445]),
       np.array([ 17.91147242,  17.2770623 ,  17.0320501 , 
16.73729491,  16.4910479 ])], dtype=object)

I wish to slice the first element of each sub-array so I can perform
basic statistics (mean, sd, etc...0).

How can I do that for large data without resorting to loops? Here's the
result I want with a loop:

    s = np.zeros(4)
    for i in np.arange(4):
        s[i] = a[i][0]

    array([ 17.56578416,  17.9002445 ,  17.90086839,  17.91147242])

Thank you


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