Dynamically naming new table columns in a loop
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I'm inputting large data sets (~300 x 500) and need to act on the data creating lots of new variables. I've got syntax for adding, deleting, moving columns but can't find anything that talks about how to assign values to a column being created in the same line. There are so many columns that need to be acted on in the same way I really need loops. The closest seems to be incorporating eval, but it's not doing what I expect. As a simplified example:
summaryTable = readtable(strcat(path,'/',name,ext)); %import big csv file
%the imported column names are ["VarA1"; "VarA2"; "VarB1"; "VarB2"]
for i = 1:2
eval(strcat(summaryTable, '.Multiplied', string(i))) = eval(strcat('summaryTable.VarA', string(i))) .* eval(strcat('summaryTable.VarB', string(i)))
end
The eval statements work on the right, but assigning the new variable doesn't. What's the secret?
采纳的回答
"What's the secret?"
Very simple: don't use EVAL.
It is simpler, much more robust, and much more efficient to add fields using the syntaxes given in the documentation:
For example:
T = readtable(..)
for k = 1:2
F0 = "Mult"+k;
F1 = "VarA"+k;
F2 = "VarB"+k;
T.(F0) = T.(F1) .* T.(F2);
end
更多回答（1 个）
Use dynamic field names (the documentation is for structs, but it works for tables too (evidently)):
VarA1 = [1 2 3].';
VarA2 = [1 2 3].'+3;
VarB1 = [1 2 3].'+6;
VarB2 = [1 2 3].'+9;
summaryTable = table(VarA1,VarA2,VarB1,VarB2);
display(summaryTable);
for i = [1 2]
str = num2str(i);
summaryTable.(['Multiplied' str]) = summaryTable.(['VarA' str]) .* summaryTable.(['VarB' str]);
end
display(summaryTable);
1 个评论
Link to the correct documentation (for tables, not structs):
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