Numpy Array Get row index searching by a row

Question

I am new to numpy and I am implementing clustering with random forest in python. My question is:

How could I find the index of the exact row in an array? For example

[[ 0.  5.  2.]
 [ 0.  0.  3.]
 [ 0.  0.  0.]]

and I look for [0. 0. 3.] and get as result 1(the index of the second row).

Any suggestion? Follows the code (not working...)

    for index, element in enumerate(leaf_node.x):
        for index_second_element, element_two in enumerate(leaf_node.x):
            if (index <= index_second_element):
                index_row = np.where(X == element)
                index_column = np.where(X == element_two)
                self.similarity_matrix[index_row][index_column] += 1

You should provide Short, Self Contained, Correct (Compilable), Example sscce.org. Not to mention that 'not working' is not a description of the problem. — zero323
– zero323, Commented Sep 21, 2013 at 0:01

Daniel · Accepted Answer · 2013-09-21 00:53:10Z

76

Why not simply do something like this?

>>> a
array([[ 0.,  5.,  2.],
       [ 0.,  0.,  3.],
       [ 0.,  0.,  0.]])
>>> b
array([ 0.,  0.,  3.])

>>> a==b
array([[ True, False, False],
       [ True,  True,  True],
       [ True,  True, False]], dtype=bool)

>>> np.all(a==b,axis=1)
array([False,  True, False], dtype=bool)

>>> np.where(np.all(a==b,axis=1))
(array([1]),)

answered Sep 21, 2013 at 0:53

Daniel

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4 Comments

root-11 Over a year ago

Can you do that to with wildcards - say if the first "0." would be permitted as "any value" ?

Daniel Over a year ago

If I understand you correctly try: a[:,1:] == np.array([0, 3]) instead of a == b. So what we do is just slice off the first column and compare as shown.

root-11 Over a year ago

Ok - so wildcards are out of the question. Excellent clarification. Thx

Shuangjun Liu Over a year ago

Does np.where really return index? Why the document shows a different thing? numpy.org/doc/stable/reference/generated/numpy.where.html

Jorg from Jorgia · Accepted Answer · 2021-11-11 11:08:23Z

0

a=[[ 0.,5.,  2.],
[ 0. , 0.,  3.],
[ 0.,  0.,  0.]]

for i in enumerate(a):
    if i[1]==[ 0. , 0.,  3.]:
        print(i[0])

answered Nov 11, 2021 at 11:08

Jorg from Jorgia

1

1 Comment

Community Over a year ago

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