How to batch convert table columns to categorical
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Giancarlo Storti Gajani
2018년 9월 19일
댓글: Giuseppe Degan Di Dieco
2021년 7월 6일
I have a large table (large number of columns and very large number of rows), many of these columns contain simple cell arrays with a very limited number of different options (such as 'ON" and 'OFF' or similar).
I would like to convert all these columns to categorical in an automated way, i.e. extracting column names from
Table.Properties.VariableNames
and not explicitly writing the (large) number of column names in dot notation.
I have seen that
>> ddd2 = categorical(MyTable{:,MyTable.Properties.VariableNames(1)});
works fine (i.e. ddd2 is a correct categorical array), but, at this point, I cannot put this categorical array back in my table. I tried:
>> MyTable{:,MyTable.Properties.VariableNames{1}}= ddd2;
The following error occurred converting from categorical to cell:
Conversion to cell from categorical is not possible.
but it returns the error you see above... On the other hand, if I use dot notation it works fine, i.e.
MyTable.Column1 = ddd2;
yields the desired results. I found a workaround, that works perfectly, but I would like to know if there is a more direct and elegant way to solve this problem.... this is the workaround:
sz0=size(MyTable);
kk=0;
for( i=1:sz0(2) )
if( iscell(MyTable{:,i}) )
ddd2 = categorical(MyTable{:,MyTable.Properties.VariableNames(i)});
eval(sprintf('MyTable.%s = ddd2;',MyTable.Properties.VariableNames{i}));
kk = kk+1;
end
end
fprintf( ' %d columns transformed to categorical\n', kk );
it works...
댓글 수: 1
Giuseppe Degan Di Dieco
2021년 7월 6일
Dear Giancarlo,
thanks for your tip on including the Table.Properties.VariableNames in a for loop. You know, it was the easy to create a cell array for the 'vars' input of the change variable types built-in function.
Best.
채택된 답변
Sean de Wolski
2018년 9월 19일
In 18b there is a convenience function to do exactly this:
Note, that it may be possible to just create your table with categoricals. How are you creating the table?
댓글 수: 7
Giuseppe Degan Di Dieco
2021년 7월 6일
Dear Sean,
thank you. You reminded me of the built-in function, best!
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