Sorting Files Sequentually

QUESTION: I am trying to create an animation of 15 TIFF files I have in a file folder. The files are named sequentually, like this: image1.tif, image2.tif, ..., image14.tif, image15.tif. I obtain the file names with File_Search. But when I cycle through the files in a loop, they are in the wrong order!

Worse than that, they are in the wrong order even if I sort them with the IDL Sort routine! What is wrong with this code?

   IDL> files = File_Search('*.tif', COUNT=count)
   IDL> sortedFiles = files[Sort(files)]
   IDL> FOR j=0,count-1 DO Print, sortedFiles[j]
           image1.tif
           image10.tif
           image11.tif
           image12.tif
           image13.tif
           image14.tif
           image15.tif
           image3.tif
           image4.tif
           image5.tif
           image6.tif
           image7.tif
           image8.tif
           image9.tif

ANSWER: Yes, you are correct that the files that are returned from File_Search are not in any guaranteed order. And to sort these file names correctly the file name number should be the same length for each file, using leading zeros if necessary. The way your files are named is going to make this sorting task more difficult for you, and you should consider naming the files correctly if you can.

But, sometimes this is not possible and we have to carry on anyway. If this is your situation, then you are going to have to extract the file number from each file name, and use the file numbers that you extract from the files to do your sorting. The code will look something like this.

   IDL> rootnames = File_Basename(files, '.tif')
   IDL> numbers = Long(StrMid(rootnames,5))
   IDL> sortedFiles = files[Sort(numbers)]
   IDL> FOR j=0,count-1 DO Print, sortedFiles[j]
           image1.tif
           image2.tif
           image3.tif
           image4.tif
           image5.tif
           image6.tif
           image7.tif
           image8.tif
           image9.tif
           image10.tif
           image11.tif
           image12.tif
           image13.tif
           image14.tif
           image15.tif

Version of IDL used to prepare this article: IDL 7.0.1.