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javascriptarrays
Babra Cunningham
Babra Cunningham

Reputation: 2967

Javascript tracking the differences between elements in an array?

I have the following simple array: 

my_array = [1, 11, 44, 4]

I want to produce a new array consisting of the difference between these elements, so it would be:

diff_array = [10, 33, 40]

What's the best way of going about this?

Upvotes: 2

Views: 211

Answers (4)

Redu
Redu

Reputation: 26191

Normally one can do this with .reduce() but just for fun lets get some functional.

var myArray = [1, 11, 44, 4],
       diff = a => a.length > 1 ? [Math.abs(a[1]-a[0])].concat(diff(a.slice(1))) : [];

console.log(diff(myArray));

Note: The above code is just for demonstration purposes. In your daily JS life you shouldn't do things like this. Use a whatever loop you like but never use recursion in your JS code. You want to see what i mean? Feed this array.

var myArray = Array(1000000).fill().map(_ => ~~(Math.random()*100+1));

It will beautifully crash your browser's tab. Peah..!

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386680

You could use Array#reduce for iterating and take the absolute delta for pushing to the result array.

Basically you need array.length - 1 deltas and iteration. In this case 3. Reduce takes, if no start value is given, the first two elements and iterates the wanted length. And while it needs the last value for the delta, the last value is returned.

At the end, the returned value of reduce is discarded, becuase it is not used anymore.

1    11    44    4   values
 \  /  \  /  \  /
  10    33    40     Math.abs(delta)


var array = [1, 11, 44, 4],
    result = [];
    
array.reduce(function (a, b) {
    result.push(Math.abs(a - b));
    return b; 
});

console.log(result);

Upvotes: 6

Ahmed Eid
Ahmed Eid

Reputation: 4814

here is a simple solution with a plain old for loop 

array = [1, 11, 44, 4]
diff = []

for(var i = 1 ; i < array.length ; i++){
  diff.push(Math.abs(array[i] - array[i-1]))
}

basically you loop starting at the second element of the array ,, and subtract from from the prev and pushing to the new array .

Upvotes: 3

pranavjindal999
pranavjindal999

Reputation: 3047

use this function, pass it the input array, returns the required array.

function diff(array){
 var out = []
 for (var i = 0; i < array.length-1; i++) {
    out.push(Math.abs(array[i+1]-array[i]))
 }
 return out;
}

Upvotes: 2

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