How do I find array elements that meet some condition with strcmp?

Hi,

I have a vector of image files. I would like to pull out only a subset of these files which meet a certain condition. The file names are numbers, and are organized (i.e., files 1100-1199 are one group, 1200-1299 another, etc.). I tried to use the find function, but since these are file names and not simply numbers, I don't think that will work. Should I use "strcmp"?. I'm not familiar with it. My code I have so far is below... Thanks! I'm working with Psychtoolbox.

close all;
clear all;
clc % clear command window

% Images

Images = {'1100.bmp';'1202.bmp';'1203.bmp';...}

% Shuffle images 

Images=Shuffle(Images)

% Display matched image 

MatchedImages=find(Images(Images<='1399' & Images>='1300'))

RandomMatchedImage = MatchedImages{ceil(rand(1)*length(MatchedImages))}

...

sca;
imagedata=imread(RandomMatchedImage);
win=Screen('OpenWindow',0);
black=BlackIndex(win);
Screen('FillRect', win, black);
TexturePointer=Screen('MakeTexture',win,imagedata);
clear imagedata;
Screen('DrawTexture',win,TexturePointer);
Screen('Flip',win);
WaitSecs(10);
sca;

Answer 1

[Guillaume]

Unfortunately, matlab's strcmp is less functional than C's strcmp and can't really be used for the sort of comparison you want. You have several options though:

If all you want to do is group the filename by their hundred, you could just compare the first two digits of the filenames, with strncmp:

MatchedImage = Images(strncmp(Images, '13', 2)); %get all images that start with '13'

This won't work if you want something finer grained than thousand, hundred, decade, or unit. For that, you could use a regular expression and test if it match with isempty.

Finally, you could convert the numeric part of your strings into double and do the comparison based on that. You can use str2double but you need to make sure your strings are just numbers. For that a simple regex would suffice:

ImageNumbers = str2double(regexp(Images, '\d+', 'match', 'once'));
MatchedImages = Images(ImageNumbers <= 1399 & ImageNumbers >= 1300);

This latter option gives you the most flexibility.

[Chelsea]

Thanks!!