Access to element in array

Question

How I can access to the element in this array or matrix

array([[-0.0359075 ,  0.09684904, -0.03384908,  0.11583249, -0.06620416,
         0.31124461,  0.2244373 , -0.22074385,  0.2731958 ,  0.35207385,
        -0.0232635 ,  0.01991997, -0.14457113, -0.22119096, -0.23231329,
        -0.25554115,  0.20723027,  0.21642838,  0.17261602, -0.14479494,
        -0.02729147,  0.28598186, -0.14462787, -0.06030619,  0.10610376,
         0.04492712, -0.03452296, -0.079672  , -0.13708481, -0.04986167,
        -0.25361556, -0.03039704]], dtype=float32)

If this matrix is r then when I r[4] to access forth element I received

IndexError: index 1 is out of bounds for axis 0 with size 1

when I tried to access using this command r(4) I received

TypeError: 'numpy.ndarray' object is not callable

Use [4], ( ) is the function call operator in Python (as it is in many languages). — cdarke
– cdarke, Commented Mar 25, 2016 at 9:18

Anton Protopopov · Accepted Answer · 2016-03-25 09:23:36Z

2

You've got an index error because you have vector but not array:

r = np.array([[-0.0359075 ,  0.09684904, -0.03384908,  0.11583249, -0.06620416,
         0.31124461,  0.2244373 , -0.22074385,  0.2731958 ,  0.35207385,
        -0.0232635 ,  0.01991997, -0.14457113, -0.22119096, -0.23231329,
        -0.25554115,  0.20723027,  0.21642838,  0.17261602, -0.14479494,
        -0.02729147,  0.28598186, -0.14462787, -0.06030619,  0.10610376,
         0.04492712, -0.03452296, -0.079672  , -0.13708481, -0.04986167,
        -0.25361556, -0.03039704]], dtype=np.float32)

In [57]: r.shape
Out[57]: (1, 32)

To get 4-th elemen you need to call 3 for 2nd axis, because indices started from 0:

In [58]: r[0,3]
Out[58]: 0.11583249

Or you could use reshape to make array from your vector:

In [65]: r.reshape(r.size, 1)[3]
Out[65]: array([ 0.11583249], dtype=float32)

Note: You could find a lot of useful information about indexing from docs

edited Mar 25, 2016 at 9:23

answered Mar 25, 2016 at 9:21

Anton Protopopov

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1 Comment

Chris Wesseling Over a year ago

It may be helpful to say that in python r[0, 3] actually means r[(0, 3)]. (edit: but that's mentioned in the docs, you pointed to.)

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