MATLAB: Quick conversion of a large (and with mixed data types) cell array into a numerical array

cell array of character vectorsnumeric arrayquick conversion

Hi, I have a 800'000 x 20 cell array and I would like to convert it into a 800'000 x 20 double precision array.
My cell array has the following features:
  • it is a mix of data types, i.e. some columns are character vectors (which represent numbers) and some columns are numbers.
  • within a column of character vectors, the number of characters is different among the rows.
Here, an example/part of my cell array:
a =
  10×3 cell array
    {'1170790,889999999897555'}    {'1009,697999999999979'}    {[ 1]}
    {'1170260,709000000031665'}    {'869,886999999999944' }    {[ 2]}
    {'1181959,743999999947846'}    {'504,125999999999976' }    {[ 3]}
    {'1174019,564000000013039'}    {'674,142000000000053' }    {[ 4]}
    {'1173729,793000000063330'}    {'689,635999999999967' }    {[ 5]}
    {'1181555,257999999914318'}    {'509,391999999999996' }    {[ 6]}
    {'1180374,280000000027940'}    {'538,126999999999953' }    {[ 7]}
    {'1180124,550999999977648'}    {'568,719000000000051' }    {[ 8]}
    {'1179305,570999999996275'}    {'626,528999999999996' }    {[ 9]}
    {'1177132,448000000091270'}    {'705,443999999999960' }    {[10]}
Any suggestion to quickly/efficiently convert this (mixed data type) cell array into a numerical array, possibly without using str2double() ?
Just for information: among my attempts for conversion, I found that str2double() is very slow and
>> cell2mat(a(:,2))
Error using cat
Dimensions of arrays being concatenated are not consistent.
Error in cell2mat (line 83)
            m{n} = cat(1,c{:,n});
and
>> str2num(char(a(:,3)))
Error using char
Cell elements must be character arrays.

Best Answer

This is likely to be faster than str2double. Use a decimal point rather than a decimal comma for more speed.
>> C = {'1170790,889999999897555','1009,697999999999979',1;'1170260,709000000031665','869,886999999999944',2;'1181959,743999999947846','504,125999999999976',3;'1174019,564000000013039','674,142000000000053',4;'1173729,793000000063330','689,635999999999967',5;'1181555,257999999914318','509,391999999999996',6;'1180374,280000000027940','538,126999999999953',7;'1180124,550999999977648','568,719000000000051',8;'1179305,570999999996275','626,528999999999996',9;'1177132,448000000091270','705,443999999999960',10}
C = 
    '1170790,889999999897555'    '1009,697999999999979'    [ 1]
    '1170260,709000000031665'    '869,886999999999944'     [ 2]
    '1181959,743999999947846'    '504,125999999999976'     [ 3]
    '1174019,564000000013039'    '674,142000000000053'     [ 4]
    '1173729,793000000063330'    '689,635999999999967'     [ 5]
    '1181555,257999999914318'    '509,391999999999996'     [ 6]
    '1180374,280000000027940'    '538,126999999999953'     [ 7]
    '1180124,550999999977648'    '568,719000000000051'     [ 8]
    '1179305,570999999996275'    '626,528999999999996'     [ 9]
    '1177132,448000000091270'    '705,443999999999960'     [10]
>> X = cellfun('isclass',C,'char'); % slower: cellfun(@ischar,C)
>> M = nan(size(C));
>> M(~X) = [C{~X}]; % numeric data
>> M(X)  = sscanf(strrep(sprintf(' %s',C{X}),',','.'),'%f') % character data
M =
               1170790.890                  1009.698                         1
               1170260.709                   869.887                         2
               1181959.744                   504.126                         3
               1174019.564                   674.142                         4
               1173729.793                   689.636                         5
               1181555.258                   509.392                         6
               1180374.280                   538.127                         7
               1180124.551                   568.719                         8
               1179305.571                   626.529                         9
               1177132.448                   705.444                        10
If the intermediate character vector does not fit into memory then simply do the above for each column of C.
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