Delete zeros from a sparse array [duplicate]
This question already has an answer here:
How to prevent a SparseArray entry from being specified when it coincides with the default value?
1 answer
Why doesn't SparseArray automatically remove zero entries? The code
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0]
r //ArrayRules
returns
{{1}->-11,{3}->0,{5}->0,{7}->0,{9}->-99,{11}->0,{2}->22,{13}->1313,{_}->0}
instead of
{{1}->-11,{9}->-99,{2}->22,{13}->1313,{_}->0}.
Is there a nice way to get rid of zero entries? For instance, when I perform Gaussian elimination on $A!in!mathbb{Z}^{mtimes n}_2$, I use A = Mod[A, 2];, and suddenly many entries are zero. I don't want to waste memory on them.
Of course I could use
A = SparseArray[DeleteCases[ArrayRules[A], #[[2]] == 0&], {m,n}]
but it seems clumsy to use this often.
Also, when I have a very long sparse row that gets updated frequently and fills up somewhat (Gaussian elimination), is it better to use SparseArray with + or Association with Merge?
matrix associations sparse-arrays rule
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
marked as duplicate by Henrik Schumacher, Lukas Lang, Niki Estner, LCarvalho, anderstood 12 hours ago
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
add a comment |
This question already has an answer here:
How to prevent a SparseArray entry from being specified when it coincides with the default value?
1 answer
Why doesn't SparseArray automatically remove zero entries? The code
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0]
r //ArrayRules
returns
{{1}->-11,{3}->0,{5}->0,{7}->0,{9}->-99,{11}->0,{2}->22,{13}->1313,{_}->0}
instead of
{{1}->-11,{9}->-99,{2}->22,{13}->1313,{_}->0}.
Is there a nice way to get rid of zero entries? For instance, when I perform Gaussian elimination on $A!in!mathbb{Z}^{mtimes n}_2$, I use A = Mod[A, 2];, and suddenly many entries are zero. I don't want to waste memory on them.
Of course I could use
A = SparseArray[DeleteCases[ArrayRules[A], #[[2]] == 0&], {m,n}]
but it seems clumsy to use this often.
Also, when I have a very long sparse row that gets updated frequently and fills up somewhat (Gaussian elimination), is it better to use SparseArray with + or Association with Merge?
matrix associations sparse-arrays rule
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
marked as duplicate by Henrik Schumacher, Lukas Lang, Niki Estner, LCarvalho, anderstood 12 hours ago
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
3
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just applySparseArrayagain.
– Szabolcs
Dec 30 '18 at 9:11
add a comment |
This question already has an answer here:
How to prevent a SparseArray entry from being specified when it coincides with the default value?
1 answer
Why doesn't SparseArray automatically remove zero entries? The code
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0]
r //ArrayRules
returns
{{1}->-11,{3}->0,{5}->0,{7}->0,{9}->-99,{11}->0,{2}->22,{13}->1313,{_}->0}
instead of
{{1}->-11,{9}->-99,{2}->22,{13}->1313,{_}->0}.
Is there a nice way to get rid of zero entries? For instance, when I perform Gaussian elimination on $A!in!mathbb{Z}^{mtimes n}_2$, I use A = Mod[A, 2];, and suddenly many entries are zero. I don't want to waste memory on them.
Of course I could use
A = SparseArray[DeleteCases[ArrayRules[A], #[[2]] == 0&], {m,n}]
but it seems clumsy to use this often.
Also, when I have a very long sparse row that gets updated frequently and fills up somewhat (Gaussian elimination), is it better to use SparseArray with + or Association with Merge?
matrix associations sparse-arrays rule
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
This question already has an answer here:
How to prevent a SparseArray entry from being specified when it coincides with the default value?
1 answer
Why doesn't SparseArray automatically remove zero entries? The code
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0]
r //ArrayRules
returns
{{1}->-11,{3}->0,{5}->0,{7}->0,{9}->-99,{11}->0,{2}->22,{13}->1313,{_}->0}
instead of
{{1}->-11,{9}->-99,{2}->22,{13}->1313,{_}->0}.
Is there a nice way to get rid of zero entries? For instance, when I perform Gaussian elimination on $A!in!mathbb{Z}^{mtimes n}_2$, I use A = Mod[A, 2];, and suddenly many entries are zero. I don't want to waste memory on them.
Of course I could use
A = SparseArray[DeleteCases[ArrayRules[A], #[[2]] == 0&], {m,n}]
but it seems clumsy to use this often.
Also, when I have a very long sparse row that gets updated frequently and fills up somewhat (Gaussian elimination), is it better to use SparseArray with + or Association with Merge?
This question already has an answer here:
How to prevent a SparseArray entry from being specified when it coincides with the default value?
1 answer
matrix associations sparse-arrays rule
matrix associations sparse-arrays rule
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
edited Dec 30 '18 at 16:51
m_goldberg
84.3k872195
84.3k872195
asked Dec 30 '18 at 2:44
Leon
371111
asked Dec 30 '18 at 2:44
Leon
371111
asked Dec 30 '18 at 2:44
Leon
371111
371111
marked as duplicate by Henrik Schumacher, Lukas Lang, Niki Estner, LCarvalho, anderstood 12 hours ago
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by Henrik Schumacher, Lukas Lang, Niki Estner, LCarvalho, anderstood 12 hours ago
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
3
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just applySparseArrayagain.
– Szabolcs
Dec 30 '18 at 9:11
add a comment |
3
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just applySparseArrayagain.
– Szabolcs
Dec 30 '18 at 9:11
3
3
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just apply
SparseArray again.– Szabolcs
Dec 30 '18 at 9:11
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just apply
SparseArray again.– Szabolcs
Dec 30 '18 at 9:11
add a comment |
1 Answer
1
active
oldest
votes
You can just apply SparseArray to a SparseArray object to normalize it. For your example:
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0];
SparseArray[r] //ArrayRules
{{1} -> -11, {2} -> 22, {9} -> -99, {13} -> 1313, {_} -> 0}
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
For simulating a row that changes and fills up somewhat, is it better to useSparseArraywith+orAssociationwithMerge?
– Leon
Dec 30 '18 at 22:34
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
You can just apply SparseArray to a SparseArray object to normalize it. For your example:
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0];
SparseArray[r] //ArrayRules
{{1} -> -11, {2} -> 22, {9} -> -99, {13} -> 1313, {_} -> 0}
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
For simulating a row that changes and fills up somewhat, is it better to useSparseArraywith+orAssociationwithMerge?
– Leon
Dec 30 '18 at 22:34
add a comment |
You can just apply SparseArray to a SparseArray object to normalize it. For your example:
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0];
SparseArray[r] //ArrayRules
{{1} -> -11, {2} -> 22, {9} -> -99, {13} -> 1313, {_} -> 0}
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
For simulating a row that changes and fills up somewhat, is it better to useSparseArraywith+orAssociationwithMerge?
– Leon
Dec 30 '18 at 22:34
add a comment |
You can just apply SparseArray to a SparseArray object to normalize it. For your example:
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0];
SparseArray[r] //ArrayRules
{{1} -> -11, {2} -> 22, {9} -> -99, {13} -> 1313, {_} -> 0}
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
You can just apply SparseArray to a SparseArray object to normalize it. For your example:
a = SparseArray[{2->22,3->33,5->55,7->77,11->1111,13->1313},13];
b = SparseArray[{1->11,3->33,5->55,7->77,9->99,11->1111},13];
r = DeleteCases[a-b,0];
SparseArray[r] //ArrayRules
{{1} -> -11, {2} -> 22, {9} -> -99, {13} -> 1313, {_} -> 0}
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
answered Dec 30 '18 at 3:06
Carl Woll
67.1k388175
67.1k388175
For simulating a row that changes and fills up somewhat, is it better to useSparseArraywith+orAssociationwithMerge?
– Leon
Dec 30 '18 at 22:34
add a comment |
For simulating a row that changes and fills up somewhat, is it better to useSparseArraywith+orAssociationwithMerge?
– Leon
Dec 30 '18 at 22:34
For simulating a row that changes and fills up somewhat, is it better to use
SparseArray with + or Association with Merge?– Leon
Dec 30 '18 at 22:34
For simulating a row that changes and fills up somewhat, is it better to use
SparseArray with + or Association with Merge?– Leon
Dec 30 '18 at 22:34
add a comment |
3
It does not do it automatically because rebuilding a sparse array is expensive. It is left to you to decide when you want to rebuild it and eliminate unnecessary entries. Just apply
SparseArrayagain.– Szabolcs
Dec 30 '18 at 9:11