Extracting rows from a matrix based on values in columns
1 vue (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Following on from this question
I have a large number of conditions lets say i needed 28 different values in the columns to find, how would i do that without finding the indices in 28 different lines, not sure how to do the for loop? :/
0 commentaires
Réponses (1)
Stephen23
le 8 Mai 2016
Modifié(e) : Stephen23
le 8 Mai 2016
A = [3, 0.1234;
1, 0.1345;
1, 0.1456;
2, 0.1567;
1, 0.1678;
1, 0.1789];
C = accumarray(A(:,1),A(:,2),[],@(n){n});
Which places each collection into one cell of cell array C:
>> C
C =
[4x1 double]
[ 0.1567]
[ 0.1234]
>> C{1}
ans =
0.1345
0.1456
0.1678
0.1789
This will automatically create as many cells as needed in one output variable C. You need to use cell array indexing to access the contents of the cells of C. Note that you should not attempt to create 28 separate variables and access them dynamically in a loop: this is very poor programming practice (sadly much loved by beginners, who think it is great) that is slow, buggy, and obfuscated:
2 commentaires
Maria445
le 8 Oct 2017
What if I have more than 1 column? That is, I want A to be a 6-by-4 matrix for example, so to have C{1} = 4-by-3 matrix?
Stephen23
le 16 Oct 2017
@Maria445: make the second input to accumarray the row indices, and change the anonymous function to use those indices to extract the required rows:
>> R = 1:size(A,1);
>> C = accumarray(A(:,1),R.',[],@(r){A(r,:)})
Voir également
Catégories
En savoir plus sur Cell Arrays dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!