How to select row or column from a matrix?

Question

Here I have a matrix a=np.array([[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15]])

I want to select all rows, but the column I want to select is from the first to the third one.

It should be [[1,2,3],[6,7,8],[11,12,13]]

However, I have ever tried a[:,[0,2]], but it shows

 array([[ 1,  3],
       [ 6,  8],
       [11, 13]])

It seems not the correct, so I tried another one a[:][0:2], it still is a wrong result.

So I want to ask if there are any function or method can fix the problem?

score 1 · Accepted Answer · answered Jun 10 '18 at 11:01

1

Sounds like you are looking for a[:, 0:3]:

In [4]: a[:, 0:3]
Out[4]:
array([[ 1,  2,  3],
       [ 6,  7,  8],
       [11, 12, 13]])

answered Jun 10 '18 at 11:01

fuglede

Yes, this is what I want. – 陳俊良 Jun 10 '18 at 11:04
Great; if you found the answer helpful, you [can accept it](https://stackoverflow.com/help/someone-answers). – fuglede Jun 10 '18 at 11:37

score 1 · Answer 2 · answered Jun 10 '18 at 11:01

1

I think need indexing 0:3:

print (a[:,0:3])
[[ 1  2  3]
 [ 6  7  8]
 [11 12 13]]

answered Jun 10 '18 at 11:01

jezrael

score 1 · Answer 3 · answered Jun 10 '18 at 11:03

1

Try the following

a=np.array([[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15]])
a = a[:,0:3] 
print(a)
#Output
#array([[ 1,  2,  3],
#   [ 6,  7,  8],
#   [11, 12, 13]])

answered Jun 10 '18 at 11:03

Md Johirul Islam

3 Answers3