Move a portion of one table into another, smaller, table.

I have two large csv files which I have imported using readtable. The contain related data but one has many more rows than the other. I have a common column between the two. I want to pull variables from the larger one at instances where the common column matches between the two tables. Forgive my syntax a bit here since I do not have matlab on the computer I am writing the question from.

table_A.VariableNames={'x' 'y' 'z'}

table_A=[.98 .3 .9;

.94 .1 .3;

.67 .1 .3;

.56 .7 .4;

.72 .4 .3;

.64 .6 .2]

table_B.VariableNames={'x' 'q' 'e'}

table_B=[.98 -.201 -.239;

.72 -2.18 -0.05;

.67 -.228 -1.28]

So in the given example I want to take the values of y and z, in table A, where x values match those in table B, and append them onto table B. I attempted to create a logical index vector with;

X_needed=table_A.x==table_B.x

I would then use that index vector to create a table with the desired values of y and z to append onto table B.

However, when I try this I get the error that "matrix dimensions must agree". I think I can reach the solution with a loop, but there must be a better way to solve this.

Thanks for any help provided.

Answer 1

[Voss]

table_A = array2table([ ...
    .98 .3 .9;
    .94 .1 .3;
    .67 .1 .3;
    .56 .7 .4; 
    .72 .4 .3;
    .64 .6 .2], ...
    'VariableNames',{'x' 'y' 'z'})

table_A = 6×3 table
     x       y      z 
    ____    ___    ___

    0.98    0.3    0.9
    0.94    0.1    0.3
    0.67    0.1    0.3
    0.56    0.7    0.4
    0.72    0.4    0.3
    0.64    0.6    0.2

table_B = array2table([ ...
    .98 -.201 -.239;
    .72 -2.18 -0.05;
    .67 -.228 -1.28], ...
    'VariableNames',{'x' 'q' 'e'})

table_B = 3×3 table
     x        q         e   
    ____    ______    ______

    0.98    -0.201    -0.239
    0.72     -2.18     -0.05
    0.67    -0.228     -1.28

[~,idx] = ismember(table_B.x,table_A.x);

table_B{:,{'y' 'z'}} = table_A{idx,{'y' 'z'}};

disp(table_B);

     x        q         e        y      z 
    ____    ______    ______    ___    ___

    0.98    -0.201    -0.239    0.3    0.9
    0.72     -2.18     -0.05    0.4    0.3
    0.67    -0.228     -1.28    0.1    0.3

[Steve K]

I'll try this out thanks.

[Steve K]

So this definitely would have worked. Except I learned that my data doesn't have the matching column that I thought it did.