Get common root of String path and list of folders for that path

Question

I've SQLite3 database table where I store a list of paths like this:

/mnt/sdcard/folder1/a/b/file1
/mnt/sdcard/folder1/a/b/file2
/mnt/sdcard/folder1/a/b/file3
/mnt/sdcard/folder1/a/b/file4
/mnt/sdcard/folder1/a/b/file5
/mnt/sdcard/folder1/e/c/file6
/mnt/sdcard/folder2/d/file7
/mnt/sdcard/folder2/d/file8
/mnt/sdcard/file9

What I want to do is to find the common root of these paths and to get the list of first level folder (unique) of that common root.

For example

First run: parent root = null (it's the first run) common root -> /mnt/sdcard/ List of folders - folder1 - folder2

Second run (now parent root will be /mnt/sdcard/folder1/) common root -> /mnt/sdcard/folder1/ (same as parent root) List of folders - a - e

Second run (now parent root will be /mnt/sdcard/folder1/a/) common root -> /mnt/sdcard/folder1/a/b (same as parent root) List of folders -> empty (I'll get files)

Is there a way to do those filters by db or I have I to do that by code?

This question is made because I need to provide a Folder View of Android Music Library that store paths in the song db record.

Answer 1

Take a look at http://rosettacode.org/wiki/Find_common_directory_path

It's implemented in some programming languages.

This is the Java example I've tested and used for my purposes.

public class CommonPath {
    public static String commonPath(String... paths){
        String commonPath = "";
        String[][] folders = new String[paths.length][];
        for(int i = 0; i < paths.length; i++){
            folders[i] = paths[i].split("/"); //split on file separator
        }
        for(int j = 0; j < folders[0].length; j++){
            String thisFolder = folders[0][j]; //grab the next folder name in the first path
            boolean allMatched = true; //assume all have matched in case there are no more paths
            for(int i = 1; i < folders.length && allMatched; i++){ //look at the other paths
                if(folders[i].length < j){ //if there is no folder here
                    allMatched = false; //no match
                    break; //stop looking because we've gone as far as we can
                }
                //otherwise
                allMatched &= folders[i][j].equals(thisFolder); //check if it matched
            }
            if(allMatched){ //if they all matched this folder name
                commonPath += thisFolder + "/"; //add it to the answer
            }else{//otherwise
                break;//stop looking
            }
        }
        return commonPath;
    }

    public static void main(String[] args){
        String[] paths = { "/home/user1/tmp/coverage/test",
                 "/home/user1/tmp/covert/operator",
                 "/home/user1/tmp/coven/members"};
        System.out.println(commonPath(paths));

        String[] paths2 = { "/hame/user1/tmp/coverage/test",
                 "/home/user1/tmp/covert/operator",
                 "/home/user1/tmp/coven/members"};
        System.out.println(commonPath(paths2));
    }
}

Answer 2

I just had to do the same thing, but in C#. Here's my solution to finding a common root directory. You should be able to adapt it.

        public static string GetCommonRoot( params string[] paths )
    {
        int minDepth = 999;
        List<string[]> parsedPaths = new List<string[]>();
        foreach( string p in paths )
        {
            string[] parts = p.Split( '\\' );
            parsedPaths.Add( parts );
            minDepth = parts.Length < minDepth ? parts.Length : minDepth;
        }

        StringBuilder sb = new StringBuilder();
        for( int i = 0; i < minDepth; i++ )
        {
            List<string> tmp = new List<string>();
            foreach( string[] dir in parsedPaths )
            {
                tmp.Add( dir[ i ].ToLower() );
            }

            if( !AllEqual( tmp.ToArray() ) )
                break;

            sb.AppendFormat( "{0}\\", tmp[ 0 ] );
        }

        return sb.ToString();

    }

    private static bool AllEqual( params string[] strings )
    {
        bool rv = true;
        for( int i = 1; i < strings.Length; i++ )
            rv &= strings[ 0 ] == strings[ i ];

        return rv;
    }