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how to arrange data into array

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Tyler
Tyler on 7 Jan 2021
Edited: Stephen Cobeldick on 10 Jan 2021
Hi,
i have imported some matrix data into matlab and upon parsing the data i have it in 3 vectors (columns):
column 1 are the row indices (i.e.):
[1;2;3;4]
column 2 are the column indices (i.e.):
[10;11;13;15]
and column 3 are the values in the matrix associated with those indices (i.e.):
[1e-5;5e-5;10e-5;15e-5]
I'd like to arrange this into a single 2-D array of column 3 data in the row locations of column1, and column locations of column2
I could do this with a loop, but im hoping to find a more elegant / less time intensive solution. I have about a million datapoints.
Thanks alot!

  3 Comments

James Tursa
James Tursa on 7 Jan 2021
Do you know the desired size of the result up front? Or do you want to just use the max row and column indexes to determine the size of the result?
Tyler
Tyler on 10 Jan 2021
i would use the max row and column indices
Tyler
Tyler on 10 Jan 2021
turns out i can use the sparse() command, followed by the full() command to achieve my desired outcome.

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Answers (1)

Stephen Cobeldick
Stephen Cobeldick on 10 Jan 2021
Edited: Stephen Cobeldick on 10 Jan 2021
Without an intermediate sparse array:
R = [1;2;3;4];
C = [10;11;13;15];
V = [1e-5;5e-5;10e-5;15e-5];
%
S = max([R,C],[],1);
M = zeros(S); % or NAN
M(sub2ind(S,R,C)) = V % only the first 10 columns are shown below
M = 4×15
0 0 0 0 0 0 0 0 0 0.0100 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0500 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.1000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.1500

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