Partitioning a vector of doubles into cells using a second vector to index

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Remi Boros
Remi Boros 2024-10-17
评论： Remi Boros 2024-10-22
Hi all,
I would like to partition a vector of numbers into separate sub-cells, using a second vector as a list of indices. See the example below:
vectorContents = 1:5;
indexingVector = [1 1 1 2 2];
I'd like the output to be a cell array that looks like
storeCell = {[1 1 1],[2 2]}
Is there a way to achieve this using deal and other parallelized functions to avoid a for loop? My current implementation looks like this:
vectorContents = 1:5;
indexingVector = [1 1 1 2 2];
uniqueInds = unique(indexingVector);
storeCell = cell(numel(uniqueInds),1);
for ii = 1:numel(uniqueInds)
currInd = uniqueInds(ii);
currLogic = indexingVector == currInd;
storeCell{ii} = vectorContents(currLogic);
end
Thanks in advance!

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采纳的回答

Stephen23
Stephen23 2024-10-17
编辑：Stephen23 2024-10-17
Ran in:
V = 1:5;
X = [1,1,1,2,2];
C = accumarray(X(:),V(:),[],@(v){v.'})
C = 2x1 cell array
{[1 2 3]} {[ 4 5]}
or
C = groupsummary(V(:),X(:),@(v){v.'})
C = 2x1 cell array
{[1 2 3]} {[ 4 5]}
or
C = arrayfun(@(n)V(n==X),1:max(X),'Uni',0) % probably the slowest
C = 1x2 cell array
{[1 2 3]} {[4 5]}

更多回答（1 个）

Pavl M.
Pavl M. 2024-10-17
编辑：Pavl M. 2024-10-17
Ran in:
clc
clear all
close all
vectorContents = 1:7
vectorContents = 1×7
1 2 3 4 5 6 7
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
indexingVector = [1 1 1 2 2 3 3]
indexingVector = 1×7
1 1 1 2 2 3 3
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
uniqueInds = unique(indexingVector)
uniqueInds = 1×3
1 2 3
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
storeCell = cell(numel(uniqueInds),1)
storeCell = 3x1 cell array
{0x0 double} {0x0 double} {0x0 double}
%Solution with no loops:
tic
%Form vector of distinct values repetitions (acc to your custom logic):
vec = [3 2 2]; % 1D vector
storeCell = mat2cell(vectorContents,1,vec)
storeCell = 1x3 cell array
{[1 2 3]} {[4 5]} {[6 7]}
toc
Elapsed time is 0.085405 seconds.
%Ver of Stephen23 measurements
tic
C = accumarray(indexingVector(:),vectorContents(:),[],@(vectorContents){vectorContents.'})
C = 3x1 cell array
{[1 2 3]} {[ 4 5]} {[ 6 7]}
toc
Elapsed time is 0.053025 seconds.
tic
C = arrayfun(@(n)vectorContents(n==indexingVector),1:max(indexingVector),'Uni',0) % probably the slowest
C = 1x3 cell array
{[1 2 3]} {[4 5]} {[6 7]}
toc
Elapsed time is 0.162446 seconds.
tic
C = groupsummary(vectorContents(:),indexingVector(:),@(indexingVector){indexingVector.'})
C = 3x1 cell array
{[1 2 3]} {[ 4 5]} {[ 6 7]}
toc
Elapsed time is 0.156229 seconds.
%Solution with 1 loops:
tic
for ii = 1:numel(uniqueInds)
currInd = uniqueInds(ii);
currLogic = indexingVector == currInd;
storeCell{ii} = vectorContents(currLogic)
end
storeCell = 1x3 cell array
{[1 2 3]} {[4 5]} {[6 7]}
storeCell = 1x3 cell array
{[1 2 3]} {[4 5]} {[6 7]}
storeCell = 1x3 cell array
{[1 2 3]} {[4 5]} {[6 7]}
toc
Elapsed time is 0.059105 seconds.
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