How to make a third matrix with exclusive values from two other matrices, with multiple columns?

Question

I am trying to make a new matrix of n rows and 7 columns, but my code only outputs the first column.

%sample values
table_a = [161.0972   11.0000   14.0000    1.0000         0         0         0;
  163.0401    9.0000    8.0000    3.0000         0         0         0;
  163.0765   10.0000   12.0000    2.0000         0         0         0;
  163.1129   11.0000   16.0000    1.0000         0         0         0;
  165.0194    8.0000    6.0000    4.0000         0         0         0;
  165.0558    9.0000   10.0000    3.0000         0         0         0;
  165.0922   10.0000   14.0000    2.0000         0         0         0]
  
table_b = [163.0401    9.0000    8.0000    3.0000         0         0         0;
  163.0765   10.0000   12.0000    2.0000         0         0         0;
  165.0558    9.0000   10.0000    3.0000         0         0         0;
  165.0922   10.0000   14.0000    2.0000         0         0         0;
  167.0350    8.0000    8.0000    4.0000         0         0         0;
  167.0714    9.0000   12.0000    3.0000         0         0         0;
  169.0143    7.0000    6.0000    5.0000         0         0         0]


table_c = table_a(~ismember(table_a(:, 1:7), table_b(:, 1:7)));

This is what I yield:

table_c =
163.0401    
163.0765  
165.0922

This is what I expect to yield:

table_c = 
163.0401    9.0000    8.0000    3.0000         0         0         0
163.0765   10.0000   12.0000    2.0000         0         0         0
165.0922   10.0000   14.0000    2.0000         0         0         0

Pranav Hosangadi · Accepted Answer · 2020-08-10T20:20:05.290

Your code currently does this:

filter = ~ismember(table_a(:, 1:7), table_b(:, 1:7));
table_c = table_a(filter);

This selects all table_a(x) that have filter(x) = true.

You want to select the rows of table_a that fulfill the condition, but select all columns of those rows. To do this, you have to tell Matlab to select those rows, and all columns of table_a

table_c = table_a(filter, :);

Or in one line,

table_c = table_a(~ismember(table_a(:, 1:7), table_b(:, 1:7)), :);

To clarify, Matlab stores its 2D arrays as column-major arrays. With a matrix

A = [0, 1, 2;
     3, 4, 5;
     6, 7, 8];

A(i) selects the ith element in the column-major-ordered array, so A(4) would give you 1. A(i, j) selects the ith row and jth column of the matrix.

Thank you, this worked perfectly and you described it so simply. — Rachel, Aug 10 '20 at 20:22

How to make a third matrix with exclusive values from two other matrices, with multiple columns?

1 Answers1