How to get column values using indexes

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.

Answer 1

[KSSV]

LEt A be your matrix.

C5 = A(:,5);  % 5th column 
M1 = A(C5==1,1:4) ; 
M2 = A(C5==2,1:4) ; 

[Stephen john]

@KSSV This is manual method , i want it to be automatic

[KSSV]

What do you mean by automatic?

[Stephen john]

@KSSV Using a Single line you manully type

M1 = A(C5==1,1:4) ;

M2 = A(C5==2,1:4) ;

M3=A(C5==3,1:4) ;

[Stephen23]

" i want it to be automatic"

Numbered variable names are a sign that you are doing something wrong.

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

A container array (e.g. a cell array) would probably be the best approach.

Answer 2

[Voss]

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}

[Stephen john]

@_ Now you created a cell thats great, Then how can i save this as a matrix?

[Voss]

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