converting cell of strings in arry or cell of numbers

I have a cell of strings 'tsince' having dimension 143 by 1 as '4632' '0.00000000' '-1440.00000000' '-1438.00000000' '-1436.00000000' '-1434.00000000' '-1432.00000000' '-1430.00000000' '-1428.00000000' . . . . '1436.00000000' '1438.00000000' '1440.00000000'

 I want to convert it to an array or cell of numbers. I tried with str2num() but it gives the following error:

>> tsince2=str2num(tsince) ??? Error using ==> str2num at 33 Requires string or character array input.

I am new to matlab. somebody can please help out how to do this. Thanks in advance

Zohaib

Answer 1

[Jan]

A surprisingly efficient method even for very large input:

C = {'4632', '0.00000000', '-1440.00000000', '-1438.00000000', ...
     '-1436.00000000', '-1434.00000000', '-1432.00000000' '-1430.00000000', ...
     '-1428.00000000', '1436.00000000', '1438.00000000', '1440.00000000'};

S = sprintf('%s ', C{:});
D = sscanf(S, '%f');

[Todd Leonhardt]

I want to thank you for an excellent and very non-intuitive answer.

I compared this approach on a Cell array of 500k length and this approach was 16 times faster than using str2double (which itself was faster than str2num/cellfun by a factor of 2).

It seems kind of crazy that using sprintf followed by sscanf is so much faster than just using str2double, but tic/toc doesn't lie ;-)

[Keld Stefan Pedersen]

Awesome. I was struggling with converting a very large cell array of strings (MxN) to numbers and this tip nailed it. Thanks a lot Jan!

[Baasanbat Tsagaan]

Best, easy solution

[Josh Philipson]

clever. Thanks Jan!

[Oli Fairfax]

I had to make my cell array a single column then ensure empties were converted to NaN (otherwise they got lost) but this worked MUCH quicker than str2double for my example, thanks Jan!

C2 = reshape(C,[],1);
C2(cellfun(@isempty,C2)) = {'NaN'};
S = sprintf('%s ', C2{:});
D = sscanf(S, '%f');
Data = reshape(D, [], size(C,2));

Answer 2

[Nirmal Gunaseelan]

STR2NUM requires a single string to work on. You need to loop around the individual cell elements and use STR2NUM. CELLFUN is a better way of doing the same - check out the doc.

Answer 3

[Matt Tearle]

Try str2double(tsince)

Answer 4

[Dao Austin]

you may convert cell to char, then use str2num:

%given A;

C=char(A);

D=str2num(C);