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How to do matching in table format?

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SC
SC on 17 Aug 2018
Answered: Peter Perkins on 24 Aug 2018
Hi,
I have some data, putting in a matrix A:-
Col1 = [1;4;0];
Col2 = [2;5;2];
Col3 = [3;6;4];
A = [Col1,Col2,Col3]
I want to extract the rows where column 2 have the value 2 (i.e. c), and also have another output with those values being updated from 2 to 200 (i.e. d).
b=(A(:,2)==2);
c=A(b,:)
d=A;
d(b,2)=200
However, now the data I obtained is a table, instead of a matrix:-
A2 = table(Col1,Col2,Col3)
I tried to use A2 to replace A in the above codes and try to obtain c and d, but I failed.
How can I obtain c and d? Many thanks!

  1 Comment

dpb
dpb on 18 Aug 2018
If the operations on the data are more convenient as array rather than as separate variables, then create the table variable as an array instead --
A2=table(A);
If there are specific reasons for keeping separate columns because most is column/variable related but there's the occasional array operation, you can retrieve the desired columns as array--
A2=table(Col1,Col2,Col3);
a=A{:,1:3};
and a is the array equivalent to A above to operate on and then put result back into the table.

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Accepted Answer

Peter Perkins
Peter Perkins on 24 Aug 2018
b = (A2.col2 == 2); % or A2{:,2) == 2
c = A(b,:) % leave this as a table
d = A2;
d.Col2(b) = 200; % or d{b,2} = 200
There's quite a lot of documentation about table subscripting that will explain all this.

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