Javascript return the largest in loop

Question

When I have a duplicate on first part of the element I want to return the largest. I have sorted the array and it looks like:

var sortedMyArray = ["4ff02829-df7e/0", "4ff02829-df7e/10", "8c138c02-c139/37", "54be465f-0c03/41", "b2036e03-384f/4", "b2036e03-384f/32", "b2036e03-384f/35"];

My expected result is:

["4ff02829-df7e/10", "8c138c02-c139/37", "54be465f-0c03/41", "b2036e03-384f/35"];

My code so far is:

for(var i=0;i<sortedMyArray.length;i++){
                    for (var k = i + 1; k < sortedMyArray.length; k++) {
                     if(sortedMyArray[i].split('/')[0] == sortedMyArray[k].split('/')[0]){
                          console.log('First values of element equal so remove the smallest element');

                            if(sortedMyArray[i].split('/')[1]<sortedMyArray[k].split('/')[1]){
                                sortedMyArray.splice(sortedMyArray[i],1);
                            }
                        }
                     }
                  }

Paul · Accepted Answer · 2017-02-03 04:49:54Z

3

Since you're array is sorted, you can just filter out each element that has a next element with the same string up to the '/':

result = sortedMyArray.filter( function ( el, i ) {
    if ( i + 1 === sortedMyArray.length )
        return true;
    return el.split( '/' )[ 0 ] !== sortedMyArray[ i + 1 ].split( '/' )[ 0 ];
} );

This assumes that your array is sorted correctly, so you always want to keep the last entry with each prefix. Just in case, I suggest that you double check that your sorting behaves the way you want for cases ending in /2 and /10.

answered Feb 3, 2017 at 4:49

Paul

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1 Comment

user4639281 Over a year ago

"b2036e03-384f/4" comes before "b2036e03-384f/32" so the sorting algorithm looks to be correct.

Tom Coughlin · Accepted Answer · 2017-02-03 05:10:39Z

This uses Array.reduce() to put the first part of each element and the full element into an object as key/value pairs. When there's duplicate keys it compares the value after the slash to store the larger value. Then returns all the values in an array.

var sortedMyArray = ["4ff02829-df7e/0", "4ff02829-df7e/10", "8c138c02-c139/37", "54be465f-0c03/41", "b2036e03-384f/4", "b2036e03-384f/32", "b2036e03-384f/35"];

var reduced = Object.values(sortedMyArray.reduce((acc, val) => {
  const [ preSlash, postSlash ] = val.split('/');

  if (acc[preSlash]) {
    const stored = acc[preSlash].slice(acc[preSlash].indexOf('/'));
    return postSlash > stored
        ? Object.assign(acc, { [preSlash]: val })
      : acc;
  } else {
    return Object.assign(acc, { [preSlash]: val });
  }
}, {}));

console.log(Object.values(reduced));

https://jsfiddle.net/g2rkmn9m/

score 1 · Accepted Answer · 2017-02-03 07:40:04Z

1

Use Array#reduce to iterate the array with an object as the accumulator.

On each iteration split the element by the delimiter, and use the first element of the result as a property in order to either initialize it or update it to the current element.

Finally use Object.values to get an array of the unique elements.

Benchmarking shows this to be faster than both of the other methods at the time of posting.

var sorted = ["4ff02829-df7e/0", "4ff02829-df7e/10", "8c138c02-c139/37", "54be465f-0c03/41", "b2036e03-384f/4", "b2036e03-384f/32", "b2036e03-384f/35"];
var unique = sorted.reduce((u, e) => ((u[e.split('/')[0]] = e), u), {});
console.log(Object.values(unique));

edited Feb 3, 2017 at 7:40

answered Feb 3, 2017 at 6:57

user4639281

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