Manipulate Array of Objects in Javascript

Question

I am not quite sure how to articulate what I'm trying to do in the title of this post, so please forgive me if the title is misleading or too ambiguous.

I have an array of objects I have created from an oData call (this is in an SAPUI5 application). The actual objects have more than three key/value pairs, but I stripped those out to keep this example simple.

[{
  "note_type_description": "General",
  "note_date": "/Date(872850505000)/",
  "note_text": "THIS IS A SUBSIDUARY OF THAT."
}, 
{
  "note_type_description": "General",
  "note_date": "/Date(873072000000)/",
  "note_text": "Say What Now?"
}, 
{
  "note_type_description": "General",
  "note_date": "/Date(891388800000)/",
  "note_text": "Say Who Now?"
},
{
  "note_type_description": "General",
  "note_date": "/Date(891993600000)/",
  "note_text": "Say When Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(909014400000)/",
  "note_text": "Say How Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(906422400000)/",
  "note_text": "Say Valentine Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(1485907200000)/",
  "note_text": "The latest interaction."
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1477958400000)/",
  "note_text": "Some information about Person"
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1483228800000)/",
  "note_text": "Are they private or public?"
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1485907200000)/",
  "note_text": "Hope this is enough information!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1485993600000)/",
  "note_text": "Good!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1487116800000)/",
  "note_text": "Better!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1488412800000)/",
  "note_text": "Best!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1490918400000)/",
  "note_text": "Superb!"
}]

I want to iterate through the objects, and create a new array of objects containing two of each type (note_type_description) of the most recent entries (note_date) so I can render that in the UI.

I am somewhat new to JS, so I am mostly just unclear as to what array methods I would use to accomplish this. I am thinking this would start with Array.map() and go from there. Any assistance would be appreciated! I will keep plugging away at this and post any updates I have along the way!

** Update **

I used @Titus 's example, here is what it looks like after a bit of modification (switched from arrow functions to regular functions):

var oArr = [{
  "note_type_description": "General",
  "note_date": "/Date(872850505000)/",
  "note_text": "THIS IS A SUBSIDUARY OF THAT."
}, {
  "note_type_description": "General",
  "note_date": "/Date(873072000000)/",
  "note_text": "Say What Now?"
}, {
  "note_type_description": "General",
  "note_date": "/Date(891388800000)/",
  "note_text": "Say Who Now?"
}, {
  "note_type_description": "General",
  "note_date": "/Date(891993600000)/",
  "note_text": "Say When Now?"
}, {
  "note_type_description": "Interaction",
  "note_date": "/Date(909014400000)/",
  "note_text": "Say How Now?"
}, {
  "note_type_description": "Interaction",
  "note_date": "/Date(906422400000)/",
  "note_text": "Say Valentine Now?"
}, {
  "note_type_description": "Interaction",
  "note_date": "/Date(1485907200000)/",
  "note_text": "The latest interaction."
}, {
  "note_type_description": "Company Information",
  "note_date": "/Date(1477958400000)/",
  "note_text": "Some information about Person"
}, {
  "note_type_description": "Company Information",
  "note_date": "/Date(1483228800000)/",
  "note_text": "Are they private or public?"
}, {
  "note_type_description": "Company Information",
  "note_date": "/Date(1485907200000)/",
  "note_text": "Hope this is enough information!"
}, {
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1485993600000)/",
  "note_text": "Good!"
}, {
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1487116800000)/",
  "note_text": "Better!"
}, {
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1488412800000)/",
  "note_text": "Best!"
}, {
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1490918400000)/",
  "note_text": "Superb!"
}];

var sortedArr = oArr.sort(function(a, b) {
  b.note_date.match(/\d+/)[0] - a.note_date.match(/\d+/)[0]
});
var toRender = [];

sortedArr.forEach(function(v) {
  if (toRender.filter(function(vv) {
      return v.note_type_description == vv.note_type_description
    }).length < 2) {
    toRender.push(v);
  }
});

toRender.forEach(function(oKey) {
  console.log(oKey.note_type_description + " | " + oKey.note_text);
});

***** Update # 2 *****

Just to complete this and give context, here is what I ended up with:

    _setNotes: function(oResponse) {
        if (typeof oResponse.results !== "undefined") {
            var aAllNotes = oResponse.results;
            var aTruncNotes = [];

            var sortedNotes = aAllNotes.sort(function(a, b) {
                a = new Date(a.note_date);
                b = new Date(b.note_date);
                return a>b ? -1 : a<b ? 1 : 0;
            });

            sortedNotes.forEach(function(v) {
                if (aTruncNotes.filter(function(vv) {
                        return v.note_type_description === vv.note_type_description;
                    }).length < 2) {
                    aTruncNotes.push(v);
                }
            });
        }
        this.getView().getModel("view").setProperty("/allNotes", aAllNotes);
        this.getView().getModel("view").setProperty("/truncNotes", aTruncNotes);
    }

Now I can call the 'truncNotes' object in my UI5 XML view and it is returned as so:

Possible duplicate of Access / process (nested) objects, arrays or JSON — Liam
– Liam, Commented Mar 3, 2017 at 16:04
What do you mean the most recent entries? Also, what is stopping you from using the existing array to render your output, why can't you just use the array you have? — Dave
– Dave, Commented Mar 3, 2017 at 16:06
Using filter, map and reduce, you usually can mimic any algo from other languages iof it's not included in JS yet. Filter to create a new array containing less elements, map to create a new array with exactly the same length and reduce to transform an array into anything else, including a different array. — Shilly
– Shilly, Commented Mar 3, 2017 at 16:06
You should also post an example of what you expect your result to look like, as well as what you have tried. — vol7ron
– vol7ron, Commented Mar 3, 2017 at 16:13

Titus · Accepted Answer · 2017-03-03 16:16:00Z

One way of doing this will be to first sort your array by note_date and then, create a new array and add to it only 2 objects with the same note_type_description value.

Here is an example:

var arr = [{
  "note_type_description": "General",
  "note_date": "/Date(872850505000)/",
  "note_text": "THIS IS A SUBSIDUARY OF THAT."
}, 
{
  "note_type_description": "General",
  "note_date": "/Date(873072000000)/",
  "note_text": "Say What Now?"
}, 
{
  "note_type_description": "General",
  "note_date": "/Date(891388800000)/",
  "note_text": "Say Who Now?"
},
{
  "note_type_description": "General",
  "note_date": "/Date(891993600000)/",
  "note_text": "Say When Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(909014400000)/",
  "note_text": "Say How Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(906422400000)/",
  "note_text": "Say Valentine Now?"
},
{
  "note_type_description": "Interaction",
  "note_date": "/Date(1485907200000)/",
  "note_text": "The latest interaction."
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1477958400000)/",
  "note_text": "Some information about Person"
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1483228800000)/",
  "note_text": "Are they private or public?"
},
{
  "note_type_description": "Company Information",
  "note_date": "/Date(1485907200000)/",
  "note_text": "Hope this is enough information!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1485993600000)/",
  "note_text": "Good!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1487116800000)/",
  "note_text": "Better!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1488412800000)/",
  "note_text": "Best!"
},
{
  "note_type_description": "Relationship Strategy",
  "note_date": "/Date(1490918400000)/",
  "note_text": "Superb!"
}];

var sortedArr = arr.sort((a, b) => b.note_date.match(/\d+/)[0] - a.note_date.match(/\d+/)[0]);
var toRender = [];

sortedArr.forEach(v => {
    if(toRender.filter(vv => v.note_type_description == vv.note_type_description).length < 2){
         toRender.push(v);
    }
});

console.log(toRender);

This is not the most efficient way of doing it but it will introduce you to the JavaScript array functions like sort, filter and forEach

Thank you @Titus, I think this is pointing me in the direction I need to go. I had to convert to regular functions, as I don't have the luxury taking advantage of ES6 at this point.

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