How to convert all the rows containing char values to numbers in a table without for loop?

Hi All,

I have a table containing 1360 rows and 50000 columns. Rows from 17 until end are actually numbers but stored as 'char'. Is there any way to convert from char to numbers without a for loop?

I tried using cellfun inside a for loop and it takes forever.

for ii = 1:size(table,2)
    table{17:end, ii} = cellfun(@str2num, table{17:end, ii}, 'UniformOutput', false);
end

example table looks like this -

var1     var2     var3    var4    var5 ... var50000
'56'      ''      '56'     ''      '0' ... ........
'56'      ''      '56'     ''      '0' ... ........
 ''       '56'    '56'     ''      '0' ... ........
 ''       '56'    '56'     ''      '56'... ........
 ''       '56'    '56'    '56'     '56'... ........

Any help is appreciated, thank you al in advance.

Regards,

Savan

Answer 1

[per isakson]

Replacing str2num by str2double might help. str2num uses eval(), which is slow. str2double takes arrays as input.

%%
cac = repmat( {'1.2'}, 1,5e4 );
tic, num = str2double( cac ); toc
str = repmat( "1.2", 1,5e4 );
tic, num = str2double( str ); toc

shows

Elapsed time is 0.539569 seconds.
Elapsed time is 0.614483 seconds.

and

>> tic, num = cellfun( @str2num, cac, 'uni',true ); toc 
Elapsed time is 0.963888 seconds.

Thus str2double it will at best take forever/2. I hoped for a bigger difference.

You use 'UniformOutput',false shouldn't it be true ?