Directly perform a multiplication on certain variables in a table

Hi,

I have a table such as

x y z

a 1 2

b 3 4

a 5 6

I want to multiply rows where the first column = b by 1000 but not touch the other rows.

I know I can get the values using a logical operatior

table.x == "b"

but I wasn't sure if I can use this logical operation to multiply the rows in place on the table without touching the other rows, without doing a for loop. My table has a lot of data so a for loop through each row is quite slow. Hence I am looking for a faster way than:

for i = 1:3

if table.x(i) == "b"

table.y(i)=table.y(i)*1000;

table.z(i)=table.z(i)*1000;

else

% do nothing

end

end

Answer 1

[Stephen23]

T = cell2table({'a',1,2;'b',3,4;'a',5,6},'VariableNames',{'x','y','z'})

T = 3×3 table
      x      y    z
    _____    _    _

    {'a'}    1    2
    {'b'}    3    4
    {'a'}    5    6

idx = strcmp(T.x,'b');
T{idx,{'y','z'}} = T{idx,{'y','z'}}*1000

T = 3×3 table
      x       y       z  
    _____    ____    ____

    {'a'}       1       2
    {'b'}    3000    4000
    {'a'}       5       6

Or alternatively:

T.y(idx) = T.y(idx)*1000;

T.z(idx) = T.z(idx)*1000;

[Peter Perkins]

Even better if you can use the string type rather than a cell array of char vectors, because then

idx = strcmp(T.x,'b');

becomes the more readable

T.x == "b"