sscanf with cell array of strings

Say I have a cell array:

C = {'2_5_7';'10_2_6';'4_3_7';'3_10_11';'3_16_11'};

To extract one row as a vector of number I was using:

sscanf(C{[2]},'%d_')'

ans =

    10     2     6

Now I would like to get several rows (say 2 and 4) in form of a matrix, but this does not work.

    sscanf(C{[2 4]},'%d_')'
    

The desired output for this case should be:

ans =

    10     2     6
    3      10    11

I would like to avoid the use of a for loop.Any suggestions?

EDIT: The elements of C dont necesarilly contain only 3 number, they can contain 4 or more. ie '3_10_11_5'

[Bruno Luong]

I tell you a secret: For-loop is your true friend, Arrayfun/cellfun are your fake friends.

[Bruno Luong]

If C contains strings coding different lengths, you cannot put the result in an array, but cell array.

Answer 1

[Stephen23]

Probably the most efficient solution:

>> C = {'2_5_7';'10_2_6';'4_3_7';'3_10_11';'3_16_11'};
>> X = [2,4];
>> M = sscanf(sprintf(' %s',C{X}),'%d_%d_%d',[3,Inf]).'
M =
   10    2    6
    3   10   11

Or a slight simplification (if you are confident about your data):

>> M = sscanf(sprintf('%s_',C{X}),'%d_',[3,Inf]).'
M =
   10    2    6
    3   10   11

[Rub Ron]

Thanks, the elements of C dont necesarrily contain only 3 number, they can be of the form of '3_10_11_5'.

[Stephen23]

Based on the edit to the original question, where this information was added "The elements of C dont necesarilly contain only 3 number, they can contain 4 or more. ie '3_10_11_5'", assuming that all cells contain strings with the same number of numbers, then you can simply adust for the size automatically:

N = numel(sscanf(C{1},'%d_'));
M = sscanf(sprintf('%s_',C{X}),'%d_',[N,Inf]).'

[Rub Ron]

I found this way. Perhpas if there is a more straight way of doin it.

cell2mat(cellfun(@(s)sscanf(s,'%d_')', C([2 4]), 'UniformOutput', false))

[Stephen23]

"Perhpas if there is a more straight way of doin it."

Yes, the way I showed you.

Using cellfun and cell2mat will be less efficient than what I showed you. Lets try it (1e4 iterations):

Elapsed time is 0.917299 seconds. % my code
Elapsed time is 4.073263 seconds. % your code

Answer 2

[Bruno Luong]

>> C = {'2_5_7';'10_2_6';'4_3_7';'3_10_11';'3_16_11_12_20'}

C =

  5×1 cell array

    {'2_5_7'        }
    {'10_2_6'       }
    {'4_3_7'        }
    {'3_10_11'      }
    {'3_16_11_12_20'}

>> A = cellfun(@str2num, strrep(C([1,5]),'_',','), 'unif', 0)

A =

  2×1 cell array

    {1×3 double}
    {1×5 double}

>> A{:}

ans =

     2     5     7


ans =

     3    16    11    12    20

[Rub Ron]

I was trying to use this form cellfun(@str2num, strrep(C([1,5]),'_',','), 'unif', 0) to get a double instead of a cell, because in my case the elements of the cell array have the same amount of numbers.

[Bruno Luong]

If they have the same number of elements, e.g.

C = {'2_5_7';'10_2_6';'4_3_7';'3_10_11';'3_16_11_12_20'}

you can do

substring=char(C([1,3]));
substring(substring=='_')=',';
str2num(substring)
% or
str2num(char(strrep(C([1,4]),'_',',')))