I want fill NaN in one column using average of two other column but I got an error.

Hey all, I want to fill all NaNs in the column named tm_m in the all tables that store in a 1 x 71 cell array named C using an average of the exact row of 2 other columns named tmax_m and tmin_m. I read the Matlab help and I thought this must work but it gave me an error:

for i=1:length(C)
    if any(contains(C{i}.Properties.VariableNames,'tm_m'))
        C{i}{C{i}{:,'tm_m'}=NaN, 'tm_m'} = mean([C.tmax_m(isnan(C.tm_m)), C.tmin_m(isnan(C.tm_m))],2);       
    end
end

the error is :

         C{i}{C{i}{:,'tm_m'}=NaN, 'tm_m'} = mean([C.tmax_m(isnan(C.tm_m)), C.tmin_m(isnan(C.tm_m))],2);       
                            ↑
Error: Incorrect use of '=' operator. To assign a value to a
variable, use '='. To compare values for equality, use '=='.
 

Thank you.

Answer 1

[Guillaume]

The comparison operator for equality is == not =, which is exclusively for assignment.

However, you need to be aware that a NaN is never equal to anything, or greater or smaller than anything meaning that:

NaN >= NaN
NaN <= NaN
NaN == NaN

are always false.

The proper way to check for NaN is with isnan.

Overall, I'd write your code as this:

for cidx = 1:numel(C)
    if ismember('tm_m', C{cidx}.Properties.VariableNames)
        toreplace = isnan(C{cidx}.tm_m);
        C{cidx}.tm_m(toreplace) = mean(C{cidx}{toreplace, {'tmax_m', tmin_m}});
    end
end

Assuming I've undestood your code correctly. In your snippet C appears to be first a cell array of tables, then a structure.

[BN]

Dear Guillaume,

Thank you for let me know about it. unfortunately, the above code leads me to another error too

Unable to perform assignment because the left and right sides
have a different number of elements. 

I attache C.mat, I want to fill every NaN in the tm_m column in all tables by averaging of tmax_m and tmin_m column in the similar row.

tmax_m tmin_m tm_m

4 0 NaN ======= I want to be (4+0)/2

10 -2 6 (isn't NaN so I don't want to take any action)

10 0 NaN === ====== I want to be (10+0)/2 = 5

Thank you

[Guillaume]

Oops, forgot to tell mean to operate along the correct dimension (and made a typo as well, but it sounds like you corrected that). Correct code:

for cidx = 1:numel(C)
    if ismember('tm_m', C{cidx}.Properties.VariableNames)
        toreplace = isnan(C{cidx}.tm_m);
        C{cidx}.tm_m(toreplace) = mean(C{cidx}{toreplace, {'tmax_m', 'tmin_m'}}, 2);
    end
end

[BN]

Thank you