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Most reliable and fastest way to get differences between two lists

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  • Most reliable and fastest way to get differences between two lists

    I have a text file that holds a long list of number collections. I loop through the text file list capturing the rows number collection (list 1) and then have to compare that iterations number collection (list 1) against a collection of numbers from a table (list 2). The list is 300-500 rows, and the iteration collection for comparison holds 15-30 numbers. I need to determine the difference between the iteration collection (list 1) and the table collection (list 2). I know of several ways it can be done, word_subtract list 1 against list 2 and vica versa, loop through list 1 with if is_one_of(foo,list2) and vica versa and maybe others. I'd like to know others' simplest, best, favorite method for this. Thanks.

    list 1 (iteration capture from text file)

    list 2 (list from table)

    Mike W
    "I rebel in at least small things to express to the world that I have not completely surrendered"

  • #2
    Re: Most reliable and fastest way to get differences between two lists

    look at stack overflow

    Array.prototype.diff = function(a) {
        return this.filter(function(i) {return a.indexOf(i) < 0;});
    // Examples  
    [1,2,3,4,5,6].diff( [3,4,5] );  
    // => [1, 2, 6]
    ["test1", "test2","test3","test4","test5","test6"].diff(["test1","test2","test3","test4"]);  
    // => ["test5", "test6"]

    function arr_diff (a1, a2) {
        var a = [], diff = [];
        for (var i = 0; i < a1.length; i++) {
            a[a1[i]] = true;
        for (var i = 0; i < a2.length; i++) {
            if (a[a2[i]]) {
                delete a[a2[i]];
            } else {
                a[a2[i]] = true;
        for (var k in a) {
        return diff;
    console.log(arr_diff(['a', 'b'], ['a', 'b', 'c', 'd']));
    console.log(arr_diff("abcd", "abcde"));
    console.log(arr_diff("zxc", "zxc"));
    Alex Collier

    "The spread of computers and the Internet will put jobs in two categories. People who tell computers what to do, and people who are told by computers what to do"

    AA Builds from 5221_5152 to Pre-releases >> Deploying to IIS in AWS


    • #3
      Re: Most reliable and fastest way to get differences between two lists

      list_1 = "1,2,4,6,8,9,11,15,16,17,22,23,24,25,26,28,30"
      list_2 = "1,2,4,6,7,9,10,11,15,16,17,21,23,24,25,26,30"
      same =  word_in_common(comma_to_crlf(list_1),comma_to_crlf(list_2))
      ttl_list = comma_to_crlf(list_1+","+list_2)
      diff_list = sortsubstr(crlf_to_comma(word_subtract(ttl_list,same)),",","A","N")
      ? diff_list
      = "7,8,10,21,22,28"
      Which can be reduced to the one line

      diff_list = sortsubstr(crlf_to_comma(word_subtract(comma_to_crlf(list_1+","+list_2),word_in_common(comma_to_crlf(list_1),comma_to_crlf(list_2)))),",","A","N")
      ? diff_list
      = "7,8,10,21,22,28"
      Last edited by Stan Mathews; 06-11-2018, 08:40 AM.
      There can be only one.


      • #4
        Re: Most reliable and fastest way to get differences between two lists

        Nice examples. Stan, I understand yours - Get what's the same and subtract from all to get what's different. Nice! An approach that I didn't think of being too wrapped up in List Processing and neglected Character Extraction functions. Thank you.
        Mike W
        "I rebel in at least small things to express to the world that I have not completely surrendered"


        • #5
          Re: Most reliable and fastest way to get differences between two lists

          That's the best part of the message board. Throw it out there and see how someone else would solve it.

          I created a function to do it but you probably did the same.

          word_diff - 06-12-2018 -1.txt
          There can be only one.