How to Add missing items into JavaScript array?

Question

I have following JavaScript array:

[
    {
        "day": 0,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 2,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 3,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 4,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 6,
        "best_hour_of_the_day": "--",
        "appt_success_rate": "0",
        "appt_100_numbers": "0"
    }
]

And I have defined array with with representation of the days which i need in result.

var daysOfTheWeek = [0,1,2,3,4,5,6];

I would like to ask, what is the good way how to add missing items to JavaScript array?

It means add missing values 1 and 6 to get following JavaScript result:

[
    {
        "day": 0,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 1,
        "best_hour_of_the_day": "--",
        "appt_success_rate": "0",
        "appt_100_numbers": "0"
    },
    {
        "day": 2,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 3,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 4,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 5,
        "best_hour_of_the_day": "10",
        "appt_success_rate": "60",
        "appt_100_numbers": "27"
    },
    {
        "day": 6,
        "best_hour_of_the_day": "--",
        "appt_success_rate": "0",
        "appt_100_numbers": "0"
    }
]

The finally commas after the entries for day: 5 in the first example and after day: 6 in the second example are not valid syntax. — dhke
– dhke, Commented Mar 10, 2015 at 7:41
I just updated syntax to JSON. But principle should be relative same for JS and JSON. — redrom
– redrom, Commented Mar 10, 2015 at 8:08

1000111 · Accepted Answer · 2015-03-11 06:03:13Z

I am giving the solution in JAVASCRIPT :

see demo:

jsfiddle link: http://jsfiddle.net/3phba87q/

given:

var dummyData=[
        {
            day: 0,
            best_hour_of_the_day: "10",
            appt_success_rate: "60",
            appt_100_numbers: "27"
        },
        {
            day: 2,
            best_hour_of_the_day: "10",
            appt_success_rate: "60",
            appt_100_numbers: "27"
        },
        {
            day: 3,
            best_hour_of_the_day: "10",
            appt_success_rate: "60",
            appt_100_numbers: "27"
        },
        {
            day: 4,
            best_hour_of_the_day: "10",
            appt_success_rate: "60",
            appt_100_numbers: "27"
        },
        {
            day: 5,
            best_hour_of_the_day: "10",
            appt_success_rate: "60",
            appt_100_numbers: "27"
        }
    ];
var daysOfTheWeek = [0,1,2,3,4,5,6];

in order to get expected result:

var existingDays = [];
// get the existing days

for(var i=0;i<dummyData.length;i++){
    existingDays[i] = dummyData[i]['day'];
}

// check which day's data is missing; then create a dummy object and push it to the dummyData object

for(var i=0;i<daysOfTheWeek.length;i++){
   if(existingDays.indexOf(parseInt(daysOfTheWeek[i])) < 0){
       var dummyObject = {
        "day": i,
        "best_hour_of_the_day": "--",
        "appt_success_rate": "0",
        "appt_100_numbers": "0"
       };
       dummyData.push(dummyObject);
   }
}

//sort day wise ascending

dummyData.sort(function(x,y){ return parseInt(x.day) - parseInt(y.day) });

score 2 · Accepted Answer · 2015-03-11 06:43:00Z

In modern JS, this would be

function addMissingItems(days, input) {

  function get (day) { return find(day) || make(day); }
  function find(day) { return input.find(function(x) { return x.day===day; }); }
  function make(day) { return { day: day, ...}; }

  return days.map(get);
}

var newArray = addMissingItems(daysOfTheWeek, input);

This uses map to create and return an array parallel to daysOfTheWeek, where each element is the result of calling get. get tries to find an element in the input for that day, by calling find, and if that doesn't work, creates a new element for that day, by calling make.

This uses Array#find, which may or may not be available in your browser. There's a polyfill at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find. Or, you could write your own:

function findInArray(array, condition) {
    for (var i = 0; i < array.length; i++) {
        var elt = array[i];
        if (condition(elt, i, array)) return elt;
    }
}

and change the implementation of find in the code above to

return findInArray(input, function() {...});

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