file name manipulation

I have a file name that takes the form: S_1_X_Y where X can be an integer between 1-16, and Y is a letter a,b,c,d.

I want to be able to just replace the number X by a user defined value.

any help greatly appreciated. Thanks

[Jason]

Just to add, the "1" in the file name can also be 1,2,3,4.

Answer 1

[Oleg Komarov]

X = 1;
Y = 'a';
sprintf('S_1_%d_%s',X,Y)

EDIT

str = 'S_1_6_a'
x   = 3;

regexprep(str,'(_)\d+(_[abcd])', ['$1' sprintf('%d',x) '$2'])

ans =
S_1_3_a

[Jason]

Y is not a variable, its fixed by the first file I read in, and so would need to extract this from the file name

[Oleg Komarov]

I misread your request at first, now given a string name "str", it replaces the 6 in the example with the number 3.

[Jason]

but sometimes the number to be replaced can be single digit 1-9) or double digit 10-16.

[Jason]

sorry, i didn't realise you code handles this. Thanks

Answer 2

[Teja Muppirala]

NUM2STR is useful for stuff like this.

Y = {'a' 'b' 'c' 'd'}

for jj = 1:4
  for n = 1:9
    filename = ['S_1_' num2str(n) '_' Y{jj}]
  end
end

Or alternatively, if you need to have zeros in there like '001', '002', '003' then you can use SPRINTF instead of NUM2STR

n = 7;
filename = ['S_1_' sprintf('%03.f',n) '_a']

n = 61;
filename = ['S_1_' sprintf('%03.f',n) '_a']

[Oleg Komarov]

num2str supports the format:

num2str(1,'%03.f')

[Jason]

sorry, I didn't explain my question clearly. I read in a filename that takes the form S_1_X_Y e.g. S_1_6_a the "a" character can be either a,b,c,d. X can be 1 to 16..

Once this filename is read in as a string, I need to keep it exactly the same, but only change the character X to a different number between 1-16.

[Oleg Komarov]

I edited my answer. Check it out.