How to get column values using indexes

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Stephen john
Stephen john on 13 May 2022
Edited: Voss on 13 May 2022
Hello everyone, I hope you are doing well.
I have the following data, i want to seperate the four column based on the fifth column
for example if the fifth column has value 1 it the first four column values store in other matrix.
Similarly for fifth column value = 2 the first four column related to values=2 store in other matrix.

Answers (2)

KSSV
KSSV on 13 May 2022
Edited: KSSV on 13 May 2022
LEt A be your matrix.
C5 = A(:,5); % 5th column
M1 = A(C5==1,1:4) ;
M2 = A(C5==2,1:4) ;
  4 Comments
Stephen23
Stephen23 on 13 May 2022
" i want it to be automatic"
Numbered variable names are a sign that you are doing something wrong.
A container array (e.g. a cell array) would probably be the best approach.

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Voss
Voss on 13 May 2022
S = load('matlab.mat');
A = S.Dataset23;
result = splitapply(@(x){x(:,1:4)},A,findgroups(A(:,5)))
result = 5×1 cell array
{ 96×4 double} {303×4 double} { 83×4 double} { 87×4 double} { 17×4 double}
  2 Comments
Voss
Voss on 13 May 2022
Edited: Voss on 13 May 2022
The cell array contains the matrices you need. There is no reason to store them as separate matrix variables. Just access them from the cell array as needed.
S = load('matlab.mat');
A = S.Dataset23;
result = splitapply(@(x){x(:,1:4)},A,findgroups(A(:,5)))
result = 5×1 cell array
{ 96×4 double} {303×4 double} { 83×4 double} { 87×4 double} { 17×4 double}
result{1} % get the 1st matrix
ans = 96×4
1.0e+09 * 0.0000 2.6001 -0.0000 0.0000 0.0000 2.6001 -0.0000 0.0000 0.0000 2.6001 -0.0000 0.0000 0.0000 2.5997 -0.0000 0.0000 0.0000 2.5998 -0.0000 0.0000 0.0000 2.6002 -0.0000 0.0000 0.0000 2.6003 -0.0000 0.0000 0.0000 2.6004 -0.0000 0.0000 0.0000 2.6005 -0.0000 0.0000 0.0000 2.5998 -0.0000 0.0000
result{5} % get the 5th matrix
ans = 17×4
1.0e+09 * 0.0000 2.6037 -0.0000 0.0000 0.0000 2.6042 -0.0000 0.0000 0.0000 2.6044 -0.0000 0.0000 0.0000 2.6038 -0.0000 0.0000 0.0000 2.6040 -0.0000 0.0000 0.0000 2.6043 -0.0000 0.0000 0.0000 2.6039 -0.0000 0.0000 0.0000 2.6036 -0.0000 0.0000 0.0000 2.6038 -0.0000 0.0000 0.0000 2.6045 -0.0000 0.0000
3*result{5} % get the 5th matrix and multiply it by 3 (or do whatever you need to do with it)
ans = 17×4
1.0e+09 * 0.0000 7.8111 -0.0000 0.0000 0.0000 7.8126 -0.0000 0.0000 0.0000 7.8131 -0.0000 0.0000 0.0000 7.8114 -0.0000 0.0000 0.0000 7.8121 -0.0000 0.0000 0.0000 7.8129 -0.0000 0.0000 0.0000 7.8117 -0.0000 0.0000 0.0000 7.8109 -0.0000 0.0000 0.0000 7.8114 -0.0000 0.0000 0.0000 7.8134 -0.0000 0.0000

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