# How to replace leading zeroes by spaces with regexprep

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Blue on 8 Jul 2020
Commented: madhan ravi on 9 Jul 2020
Hi,
I have a basic question. I simply need to replace the leading zeroes by empty spaces in table T except for the last zero which needs to remain zero. The desired output is output. I know I should probably use regexprep but the exact synthax always throws me off. Its for exportation purposes.
a = {'1231', '0002', '0103', '0000'}';
b = {'000', '000', '000', '000'}';
c = {'0', '0', '0', '0'}';
T = table(a,b,c);
d = {'1231', ' 2', ' 103', ' 0'}';
e = {' 0', ' 0', ' 0', ' 0'}';
f = {'0', '0', '0', '0'}';
output = table(d,e,f);
Thank you,

Stephen23 on 9 Jul 2020
Edited: Stephen23 on 9 Jul 2020
>> fun = @(c)regexprep(c,'^0+(?=\d)','\${char(double(\$&)-16)}');
>> out = varfun(fun,T)
out =
Fun_a Fun_b Fun_c
______ _____ _____
'1231' ' 0' '0'
' 2' ' 0' '0'
' 103' ' 0' '0'
' 0' ' 0' '0'
Or
>> fun = @(c)regexprep(c,'^0+(?=\d)','\${repmat('' '',1,numel(\$&))}');
>> out = varfun(fun,T)
out =
Fun_a Fun_b Fun_c
______ _____ _____
'1231' ' 0' '0'
' 2' ' 0' '0'
' 103' ' 0' '0'
' 0' ' 0' '0'
madhan ravi on 9 Jul 2020
”How should the tutorial be arranged? What topics need to be covered or explained that are not already covered in the documentation?”
To be honest I don’t know how it could be arranged Stephen. But it could cover for example lots of examples which are not covered in the documentation. I will add up some additional ideas in your new thread as well because at the moment the things I learnt about Regex have slightly faded away.
“Perhaps there is already an online tutorial which describes regular expressions similar to MATLAB's, it might be easier to just link to that (if we could identifiy a well-written tutorial).“
There might be many but it wouldn’t match like you describe the concepts!

James Tursa on 8 Jul 2020
Edited: James Tursa on 8 Jul 2020
One way:
fun = @(x)sprintf(['%' num2str(numel(x)) 'd'],str2double(x));
d = cellfun(fun,a,'uni',false);
e = cellfun(fun,b,'uni',false);
f = cellfun(fun,c,'uni',false);
Blue on 9 Jul 2020
Hi. Thank you for your input but this is going to be quite slow. Thats also why I dont want to convert everything to double and then use the pad function.

Raj Kumar Bhagat on 9 Jul 2020
Edited: Raj Kumar Bhagat on 9 Jul 2020
I tried using the basic loop statements. I was able to get the required output. Check if this code helps.
if true
for i = 1: length(a)
tempoutput = [];
for j =1: length(char(a(i)))
tempchar = char(a(i))
if ~strcmp(tempchar(j),'0')
for k = j:length(tempchar)
tempoutput = [tempoutput, tempchar(k)];
end
break;
end
end
if isempty(tempoutput)
output(i)={'0'};
else
output(i) = {tempoutput};
end
end
output = output';
end
end