Find only numeric strings on cellstr array.

I'd like to know the index of the "numerical strings" within a cellstr array.

arr = {'123', 'Hola', 'my', 'String',  '', '1453', 'stay'};

A correct output will give me index 1 and 6.

isnumeric contained within cellfun doesn't work well here, I'd have to use it in combination with something else but I don't know exactly what that might be.

Any help is appreciated.

Answer 1

[Krishna Sutar]

From my understanding you want to find the indexes of the strings in the cell string array that are numerical. Here is the code which might help you:

arr = {'123', 'Hola', 'my', 'String', '', '1453', 'stay'}; 
idx = find(~isnan(str2double(arr))) 

isnumeric checks whether the datatype of the object is numeric, which in this case is string which would return false. Please refer to isnumeric and find for more information.

[Ajpaezm]

Thank you. Out of this group of good answers, this is the one I liked the most. Thanks!

[Stephen23]

Note that this code will incorrectly mark 'NaN' as not numeric.

[Ajpaezm]

@Stephen Cobeldickthank you, I understand. Luckily, the array won't have any presence of them, but in case some weird stuff happens and indeed gets populated with it, I'll be sure to use your proposal.

Answer 2

[Walter Roberson]

arr = {'123', 'Hola', 'my', 'String',  '', '1453', 'stay'};

find(~cellfun(@isempty, regexp(arr, '^\d+$', 'once')))

ans = 1×2

1 6

find(matches(arr, lineBoundary + digitsPattern + lineBoundary))

ans = 1×2

1 6

Answer 3

[Stephen23]

Writing regular expressions or pattern matching that robustly detects all valid number formats is not such a trivial task... it is more reliable to let MATLAB do the heavy lifting:

arr = {'123', 'Hola', 'my', 'String',  '', '1453', 'stay', '-1.234', 'NaN', '9e-87'};
idx = strcmpi(arr,'NaN')|~isnan(str2double(arr))

idx = 1×10 logical array
   1   0   0   0   0   1   0   1   1   1

find(idx)

ans = 1×5

1 6 8 9 10