Extracting first n columns of a numpy matrix
Question:
I have an array like this:
array([[-0.57098887, -0.4274751 , -0.38459931, -0.58593526],
[-0.22279713, -0.51723555, 0.82462029, 0.05319973],
[ 0.67492385, -0.69294472, -0.2531966 , 0.01403201],
[ 0.41086611, 0.26374238, 0.32859738, -0.80848795]])
Now I want to extract the following:
[-0.57098887, -0.4274751]
[-0.22279713, -0.51723555]
[ 0.67492385, -0.69294472]
[ 0.41086611, 0.26374238]
So basically just first 2 columns..
Answers:
If a
is your array:
In [11]: a[:,:2]
Out[11]:
array([[-0.57098887, -0.4274751 ],
[-0.22279713, -0.51723555],
[ 0.67492385, -0.69294472],
[ 0.41086611, 0.26374238]])
I know this is quite an old question –
A = [[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
Let’s say, you want to extract the first 2 rows and first 3 columns
A_NEW = A[0:2, 0:3]
A_NEW = [[1, 2, 3],
[4, 5, 6]]
Understanding the syntax
A_NEW = A[start_index_row : stop_index_row,
start_index_column : stop_index_column)]
If one wants row 2 and column 2 and 3
A_NEW = A[1:2, 1:3]
Reference the numpy indexing and slicing article – Indexing & Slicing
I have an array like this:
array([[-0.57098887, -0.4274751 , -0.38459931, -0.58593526],
[-0.22279713, -0.51723555, 0.82462029, 0.05319973],
[ 0.67492385, -0.69294472, -0.2531966 , 0.01403201],
[ 0.41086611, 0.26374238, 0.32859738, -0.80848795]])
Now I want to extract the following:
[-0.57098887, -0.4274751]
[-0.22279713, -0.51723555]
[ 0.67492385, -0.69294472]
[ 0.41086611, 0.26374238]
So basically just first 2 columns..
If a
is your array:
In [11]: a[:,:2]
Out[11]:
array([[-0.57098887, -0.4274751 ],
[-0.22279713, -0.51723555],
[ 0.67492385, -0.69294472],
[ 0.41086611, 0.26374238]])
I know this is quite an old question –
A = [[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
Let’s say, you want to extract the first 2 rows and first 3 columns
A_NEW = A[0:2, 0:3]
A_NEW = [[1, 2, 3],
[4, 5, 6]]
Understanding the syntax
A_NEW = A[start_index_row : stop_index_row,
start_index_column : stop_index_column)]
If one wants row 2 and column 2 and 3
A_NEW = A[1:2, 1:3]
Reference the numpy indexing and slicing article – Indexing & Slicing