ARRAY javascript indexOf

Question

I have a multi-dimensional array. I need some sort of loop to randomly pick a string in the array and check to see if that string contains a character. If it doesn't, then repeat until it finds one.

I wrote a for loop that checks the array for the string, BUT it starts from 0 and works its way through the array until it finds it. I need it randomly pick a string in the array...any help?

jsFiddle --> http://jsfiddle.net/hz2MZ/1/

jQuery

$(document).ready(function() {
var myarr = [{"Name":"Bob", "Char":"134"},
           {"Name":"Phil", "Char":"134"},
           {"Name":"Jane", "Char":"1"},
           {"Name":"Don", "Char":"4"},
           {"Name":"Dan", "Char":"2"},
           {"Name":"Jan", "Char":"12"},
           {"Name":"Bill", "Char":"24"},
           {"Name":"Sam", "Char":"14"},
           {"Name":"Jake", "Char":"23"},
           {"Name":"Ben", "Char":"3"}];


$('button').click(function() {
   for(var i = 0; i < myarr.length; i++) {
       if(myarr[i].Char.indexOf('2') !== -1) {
           alert("Name: " + myarr[i].Name + "\nChar: " + myarr[i].Char);
         return;
       } else {}
    } 
});

});

"I have a multi-dimensional array." No you don't. You have an array of objects. — T.J. Crowder
– T.J. Crowder, Commented Jul 5, 2013 at 21:43
I think making a copy of the array and shuffling it (or shuffling the original if there's no need to retain a specific order) is the best plan because then you stop either when you find a match or when you've checked every item. — nnnnnn
– nnnnnn, Commented Jul 5, 2013 at 21:52
"that empty branch is absolutely irrelevant" - Exactly my point. It's needless clutter, both as part of a question here and in real-world programs. — nnnnnn
– nnnnnn, Commented Jul 5, 2013 at 21:53

Johan · Accepted Answer · 2013-07-05 21:55:48Z

3

My solution

$('button').click(function () {
        var found = false;

        while (!found) {
            var randomIndex = Math.floor(Math.random() * myarr.length);
            if (myarr[randomIndex].Char.indexOf('2') !== -1) {
                alert("Name: " + myarr[randomIndex].Name + "\nChar: " + myarr[randomIndex].Char);
                found = true;
            } else {}

        }
    });

edit

Updated endless loop problem

$('button').click(function () {
    var found = false;
    var maxRandom = 20;
    var currentRandom = 0;

    while (!found && currentRandom < maxRandom) {
        var randomIndex = Math.floor((Math.random() * myarr.length));
        currentRandom++;

        if (myarr[randomIndex].Char.indexOf('2') !== -1) {
            alert("Name: " + myarr[randomIndex].Name + "\nChar: " + myarr[randomIndex].Char);
            found = true;
        } else {}
    }
}

edited Jul 5, 2013 at 21:55

answered Jul 5, 2013 at 21:47

Johan

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7 Comments

nnnnnn Over a year ago

Note that this will be an endless loop if the character searched for isn't in any of the array items.

T.J. Crowder Over a year ago

"I see TJ beat me too it" No, you caught the essential bit I missed, +1. I'd remove the entirely pointless else {} though. :-)

Johan Over a year ago

@nnnnnn there are multiple ways of handling that. The OP can decide which is best. He asked for a random way to select something, not a 100% bullet proof solution. This is a step in the right direction.

Johan Over a year ago

@T.J.Crowder I only noticed a while later, that you missed the loop. Also left the else, as the OP might want to add stuff :)

Stano Over a year ago

You could set var maxRandom = myarr.length; then decrease it-- while(maxRandom>0) and at each step swap the last item with the randomly choosen one. Then it could check all existing fields.

|

RobG · Accepted Answer · 2013-07-05 22:36:56Z

1

One approach is to copy the array, then randomly splice one member from the copy and check for the required value:

function randomValueByChar(arr, c) {
  var a = arr.slice && arr.slice();
  var i = a.length || 0;
  var t;

  while (i--) {
    t = a.splice(Math.random() * i | 0, 1);
    if (t[0].Char.indexOf(c) != -1) return t;  
  }
}

Another approach is to create an array of the indexes (e.g. [0,1,2,3…]), then randomly splice one value at a time and use it as an index to retrieve a value from the array. Both approaches will not have an infinite loop and will visit each member a maximum of once.

answered Jul 5, 2013 at 22:36

RobG

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