remove multible years from array

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Hi I am creating an array with 10 other arrays using concat. The array is a list of different years. The multiple arrays is creating multiple years for example 2 1998's. How do I only display 1 of each year in my table view. Here is a sample:

alldata = data0.concat (data1, data2, data3, data4, data5, data6, data7, data8, data9, data10, data11, data12, data13, data14, data15);
//sort data by name
//done sort data
function sortByRDate(a, b) {
   var x = a.RDate;
    var y = b.RDate;
   return ((x < y) ? -1 : ((x > y) ? 1 : 0));
//done sort data
//Rdate data to table   
This works but displays multiples of the same year, I would only like to show 1 of each year.

— asked 3 years ago by Rich Carlton
  • I have tried your solution below. If i include the ? i get an error, if I dont include it, i dont get any years in return. Is it possable the loop is writing over its self?

    — commented 3 years ago by Rich Carlton

  • I also tried just creating a new array, Still returns nothing.

    — commented 3 years ago by Rich Carlton

2 Answers

Use a javascript object as a hash array. After you concatenate the arrays, make a pass through the years to filter out the unique years. Then put those values back into the alldata array:

var unique_years = {};
var i;
for (i = 0; i < alldata.length; i++)
    var year = alldata[i];
    unique_years[year] = 1;
alldata = [];
for (var y in unique_years)
    alldata.push (y);

Simply add a unique function to you array objects.

Add the function to the Array JavaScript object
Array.prototype.unique = function(){
  return this.filter(function(s, i, a){
    return i == a.lastIndexOf(s);

Then use it on your big array

— answered 3 years ago by Christian Brousseau
answer permalink
1 Comment
  • Very slick technique. However, if I'm reading the code correctly, that is an O(n^2) operation, whereas my proposed solution should be O(n log n).

    I'm not sure if Rich's arrays are big enough to matter, but obviously, in a mobile app, we have to be cognizant of such things.

    — commented 3 years ago by Jason Priebe

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