How to get union of several immutable js Lists

Question

I have List a:

let a = Immutable.List([1])

and List b:

let b = Immutable.List([2, 3])

I want to get List union === List([1, 2, 3]) from them.

I try to merge them fist:

let union = a.merge(b); // List([2, 3])

It seems like merge method operates with indexes, not with values so overrides first item of List a with first item of List b. So, my question is what is the most simple way to get union of several lists.

Answer 1

Hello @kartik,

Merge will update the index with the current value of the merging list. So in your case you had

[0] = 1

and merged it with

[0] = 2
[1] = 3

which ended up overwriting [0]=1 with [0]=2, and then set [1]=3 resulting in your observed [2,3] array after merging.

A very simple approach to solving this would be to use concat

var a = Immutable.List([1]);
var b = Immutable.List([2,3]); 

var c = a.concat(b);

And it will work for this situation. However, if the situation is more complex, this may be incorrect. For example,

var a = Immutable.List([1,4]);
var b = Immutable.List([2,3,4]);