# How can I selectively multiplying the negative values with (-1) in an excel file?

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Md Akibul on 11 Nov 2023
Edited: dpb on 11 Nov 2023
Hi everyone, I'm trying to read an excel file which has two columns and I want to multiply the negative values of column 2 with (-1). Could anyone please help me with a code to do that? Thank you!

Star Strider on 11 Nov 2023
Edited: Star Strider on 11 Nov 2023
Multiplying the negative values of column 2 by -1 will of course create them as positive values for all the entries.
Use the abs function on column 2 to do that.

dpb on 11 Nov 2023
Edited: dpb on 11 Nov 2023
isneg=(data(:,2)<0);
data(isneg,2)=-data(isneg,2);
"Use the Force, Luke!" Here "the Force" is logical indexing, one of the most powerful features in MATLAB.
That is, of course, if you really want/need to negate a specific subset; as @Star Strider notes, for the specific operation it is the equivalent of taking the absolute value of the column in which case you can save the extra step of the indexing expression --
data(:,2)=abs(data(:,2));