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

Question

BN 2020-1-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/502674-i-want-fill-nan-in-one-column-using-average-of-two-other-column-but-i-got-an-error

评论： BN 2020-1-29

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.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Guillaume 2020-1-29

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/502674-i-want-fill-nan-in-one-column-using-average-of-two-other-column-but-i-got-an-error#answer_412732

在 MATLAB Online 中打开

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.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Guillaume 2020-1-29

在 MATLAB Online 中打开

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