# Find only numeric strings on cellstr array.

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Ajpaezm on 15 Jun 2021
Commented: Ajpaezm on 15 Jun 2021
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.

Krishna Sutar on 15 Jun 2021
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.
##### 3 CommentsShow 1 older commentHide 1 older comment
Stephen23 on 15 Jun 2021
Note that this code will incorrectly mark 'NaN' as not numeric.
Ajpaezm on 15 Jun 2021
@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.

Walter Roberson on 15 Jun 2021
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

Stephen23 on 15 Jun 2021
Edited: Stephen23 on 15 Jun 2021
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

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