Custom NumPy Slice
I have a bunch of numpy arrays that can differ in shape:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1]]
I need to select and store the indices into a variable so that I can change the array into:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 0],
[1, 1, 1, 1, 0],
[0, 0, 0, 0, 0]]
I can grab the vertical indices:
idx = np.s_[1:4, 3]
But I can't figure out how to add all of the indices from the last row and store them into idx
Update
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
python numpy numpy-slicing
asked Jan 2 at 13:31
slawslaw
1,54312454
add a comment |
I have a bunch of numpy arrays that can differ in shape:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1]]
I need to select and store the indices into a variable so that I can change the array into:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 0],
[1, 1, 1, 1, 0],
[0, 0, 0, 0, 0]]
I can grab the vertical indices:
idx = np.s_[1:4, 3]
But I can't figure out how to add all of the indices from the last row and store them into idx
Update
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
python numpy numpy-slicing
asked Jan 2 at 13:31
slawslaw
1,54312454
1
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44
add a comment |
I have a bunch of numpy arrays that can differ in shape:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1]]
I need to select and store the indices into a variable so that I can change the array into:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 0],
[1, 1, 1, 1, 0],
[0, 0, 0, 0, 0]]
I can grab the vertical indices:
idx = np.s_[1:4, 3]
But I can't figure out how to add all of the indices from the last row and store them into idx
Update
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
python numpy numpy-slicing
asked Jan 2 at 13:31
slawslaw
1,54312454
I have a bunch of numpy arrays that can differ in shape:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1],
[1, 1, 1, 1, 1]]
I need to select and store the indices into a variable so that I can change the array into:
[[1, 1, 1, 1, 1],
[1, 1, 1, 1, 0],
[1, 1, 1, 1, 0],
[0, 0, 0, 0, 0]]
I can grab the vertical indices:
idx = np.s_[1:4, 3]
But I can't figure out how to add all of the indices from the last row and store them into idx
Update
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
python numpy numpy-slicing
python numpy numpy-slicing
asked Jan 2 at 13:31
slawslaw
1,54312454
asked Jan 2 at 13:31
slawslaw
1,54312454
edited Jan 2 at 13:44
slaw
asked Jan 2 at 13:31
slawslaw
1,54312454
asked Jan 2 at 13:31
slawslaw
1,54312454
asked Jan 2 at 13:31
slawslaw
1,54312454
1,54312454
1
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44
add a comment |
1
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44
1
1
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44
add a comment |
2 Answers
2
active
oldest
votes
I'm not aware of a built-in NumPy method, but perhaps this will do:
import numpy as np
a = np.random.rand(16).reshape((4, 4)) # Test matrix (4x4)
inds_a = np.arange(16).reshape((4, 4)) # Indices of a
idx = np.s_[0:3, 3] # Vertical indices
idy = np.s_[3, 0:3] # Horizontal indices
# Construct slice matrix
bools = np.zeros_like(a, dtype=bool)
bools[idx] = True
bools[idy] = True
print(a[bools]) # Select slice from matrix
print(inds_a[bools]) # Indices of sliced elements
answered Jan 2 at 14:01
MPAMPA
77011229
add a comment |
This isn't quite using slices like you had, but numpy allows you to index with lists so you can store all the coordinates you want to change.
A = np.ones((4,5))
col = np.zeros(7,dtype='int')
row = np.zeros(7,dtype='int')
col[:5] = np.arange(5)
col[5:] = 4
row[:5] = 3
row[5:] = np.arange(1,3)
A[row,col] = 0
You could also use two slices idx1 = np.s_[1:4,3] and idx2 = np.s_[3,0:5] and apply them both.
answered Jan 2 at 13:54
tchtch
48525
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54007291%2fcustom-numpy-slice%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
I'm not aware of a built-in NumPy method, but perhaps this will do:
import numpy as np
a = np.random.rand(16).reshape((4, 4)) # Test matrix (4x4)
inds_a = np.arange(16).reshape((4, 4)) # Indices of a
idx = np.s_[0:3, 3] # Vertical indices
idy = np.s_[3, 0:3] # Horizontal indices
# Construct slice matrix
bools = np.zeros_like(a, dtype=bool)
bools[idx] = True
bools[idy] = True
print(a[bools]) # Select slice from matrix
print(inds_a[bools]) # Indices of sliced elements
answered Jan 2 at 14:01
MPAMPA
77011229
add a comment |
I'm not aware of a built-in NumPy method, but perhaps this will do:
import numpy as np
a = np.random.rand(16).reshape((4, 4)) # Test matrix (4x4)
inds_a = np.arange(16).reshape((4, 4)) # Indices of a
idx = np.s_[0:3, 3] # Vertical indices
idy = np.s_[3, 0:3] # Horizontal indices
# Construct slice matrix
bools = np.zeros_like(a, dtype=bool)
bools[idx] = True
bools[idy] = True
print(a[bools]) # Select slice from matrix
print(inds_a[bools]) # Indices of sliced elements
answered Jan 2 at 14:01
MPAMPA
77011229
add a comment |
I'm not aware of a built-in NumPy method, but perhaps this will do:
import numpy as np
a = np.random.rand(16).reshape((4, 4)) # Test matrix (4x4)
inds_a = np.arange(16).reshape((4, 4)) # Indices of a
idx = np.s_[0:3, 3] # Vertical indices
idy = np.s_[3, 0:3] # Horizontal indices
# Construct slice matrix
bools = np.zeros_like(a, dtype=bool)
bools[idx] = True
bools[idy] = True
print(a[bools]) # Select slice from matrix
print(inds_a[bools]) # Indices of sliced elements
answered Jan 2 at 14:01
MPAMPA
77011229
I'm not aware of a built-in NumPy method, but perhaps this will do:
import numpy as np
a = np.random.rand(16).reshape((4, 4)) # Test matrix (4x4)
inds_a = np.arange(16).reshape((4, 4)) # Indices of a
idx = np.s_[0:3, 3] # Vertical indices
idy = np.s_[3, 0:3] # Horizontal indices
# Construct slice matrix
bools = np.zeros_like(a, dtype=bool)
bools[idx] = True
bools[idy] = True
print(a[bools]) # Select slice from matrix
print(inds_a[bools]) # Indices of sliced elements
answered Jan 2 at 14:01
MPAMPA
77011229
answered Jan 2 at 14:01
MPAMPA
77011229
answered Jan 2 at 14:01
MPAMPA
77011229
answered Jan 2 at 14:01
MPAMPA
77011229
77011229
add a comment |
add a comment |
This isn't quite using slices like you had, but numpy allows you to index with lists so you can store all the coordinates you want to change.
A = np.ones((4,5))
col = np.zeros(7,dtype='int')
row = np.zeros(7,dtype='int')
col[:5] = np.arange(5)
col[5:] = 4
row[:5] = 3
row[5:] = np.arange(1,3)
A[row,col] = 0
You could also use two slices idx1 = np.s_[1:4,3] and idx2 = np.s_[3,0:5] and apply them both.
answered Jan 2 at 13:54
tchtch
48525
add a comment |
This isn't quite using slices like you had, but numpy allows you to index with lists so you can store all the coordinates you want to change.
A = np.ones((4,5))
col = np.zeros(7,dtype='int')
row = np.zeros(7,dtype='int')
col[:5] = np.arange(5)
col[5:] = 4
row[:5] = 3
row[5:] = np.arange(1,3)
A[row,col] = 0
You could also use two slices idx1 = np.s_[1:4,3] and idx2 = np.s_[3,0:5] and apply them both.
answered Jan 2 at 13:54
tchtch
48525
add a comment |
This isn't quite using slices like you had, but numpy allows you to index with lists so you can store all the coordinates you want to change.
A = np.ones((4,5))
col = np.zeros(7,dtype='int')
row = np.zeros(7,dtype='int')
col[:5] = np.arange(5)
col[5:] = 4
row[:5] = 3
row[5:] = np.arange(1,3)
A[row,col] = 0
You could also use two slices idx1 = np.s_[1:4,3] and idx2 = np.s_[3,0:5] and apply them both.
answered Jan 2 at 13:54
tchtch
48525
This isn't quite using slices like you had, but numpy allows you to index with lists so you can store all the coordinates you want to change.
A = np.ones((4,5))
col = np.zeros(7,dtype='int')
row = np.zeros(7,dtype='int')
col[:5] = np.arange(5)
col[5:] = 4
row[:5] = 3
row[5:] = np.arange(1,3)
A[row,col] = 0
You could also use two slices idx1 = np.s_[1:4,3] and idx2 = np.s_[3,0:5] and apply them both.
answered Jan 2 at 13:54
tchtch
48525
edited Jan 2 at 14:04
answered Jan 2 at 13:54
tchtch
48525
answered Jan 2 at 13:54
tchtch
48525
answered Jan 2 at 13:54
tchtch
48525
48525
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54007291%2fcustom-numpy-slice%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
1
I want the indices. There are times when I need to reference the values at those indices and there are times when I want to change the values at those indices. Having the indices will allow me the flexibility to do both.
– slaw
Jan 2 at 13:44