Develop Reference

Flatten arrays in an object

I have an object as below:
const USER_MAP = {
PREMIUM: ['a', 'b'],
RETAIL: ['c', 'd']
};
I would like to transform to below
[
{ segment: 'PREMIUM', id: 'a' },
{ segment: 'PREMIUM', id: 'b' },
{ segment: 'RETAIL', id: 'c' },
{ segment: 'RETAIL', id: 'd' }
]
I came up with a solution as below
const USER_MAP = {
PREMIUM: ['a', 'b'],
RETAIL: ['c', 'd']
};
const userList = Object.entries(USER_MAP).reduce((accumulator, currentValue) => {
const userListByType = currentValue[1].map(id => ({ id, segment: currentValue[0]}))
return [...accumulator, ...userListByType]
}, []);
console.log(userList);
It works but im wondering if there might be a better way to achieve above? In terms of readability as I'm nesting a map in a reduce, it seems to me that I might've complicated stuffs here

You could take Array#flatMap with a mapping of nested objects with outer key.
const
USER_MAP = { PREMIUM: ['a', 'b'], RETAIL: ['c', 'd'] },
result = Object
.entries(USER_MAP)
.flatMap(([segment, a]) => a.map(id => ({ segment, id })));
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

How to convert an array into an object of specific format?

Although it is a common problem but I couldn't find any lead to get the desired result. So here is the problem. I have the following array:
[
[ 'a' ]
[ 'a', 'b' ]
[ 'a', 'c' ]
[ 'a', 'c', 'd' ]
[ 'a', 'c', 'd', 'e' ]
]
And what I want as an end result is an object like this:
{
a: {
b: {},
c: { d: { e: {} } }
}
}
I don't understand which approach would be better to get this result and how to achieve it.

You need a double reduce, one for the outer array and one for the keys and the nesting objects.
var data = [['a'], ['a', 'b'], ['a', 'c'], ['a', 'c', 'd'], ['a', 'c', 'd', 'e']],
result = data.reduce((r, keys) => {
keys.reduce((o, k) => o[k] = o[k] || {}, r);
return r;
}, {});
console.log(result);

Filtering an array with an array of values

I have 2 arrays and i'd like to filter one array with the other. E.g. if array1 includes any of the values in array2, they should be returned.
The two arrays are:
const array1 = [a, b, c, d]
The other array, which should be filtered where 'id' is equal to any of the values in array1 is:
const array2 = [
{
id: b
title: title1
},
{
id: d
title: title2
},
{
id: f
title: title3
}
]

The easiest way is to use two for-loops. Possible not the fastest approach.
res = [];
for (var i = 0;i<array1.length;i++) {
for (var j = 0;j<array2.length;j++) {
if (array1[i] == array2[j].id) {
res.push(array2[j]);
break;
}
}
}

You could use Array.prototype.filter() and Array.prototype.indexOf():
const array1 = ['a', 'b', 'c', 'd'];
const array2 = [{
id: 'b',
title: 'title1'
}, {
id: 'd',
title: 'title2'
}, {
id: 'f',
title: 'title3'
}];
const result = array2.filter(function(x){
return array1.indexOf(x.id) !== -1;
});

Adding this missing '', You can use filter and includes methods of Array.
const array1 = ['a', 'b', 'c', 'd'];
const array2 = [
{
id: 'b',
title: 'title1'
},
{
id: 'd',
title: 'title2'
},
{
id: 'f',
title: 'title3'
}
]
const result = array2.filter(({id}) => array1.includes(id));
console.log(result);

How to add list to list in Immutable.js?

What is the best way to add List to List in Immutable.js?
concat method is working, but another way is not working.
const a = fromJS([
{
comment: 'aaaa',
who: 'a1',
buttonInfo: ['a', 'b', 'c'],
},
{
comment: 'bb',
who: 'a2',
buttonInfo: ['a', 'b', 'c'],
},
]);
const b = fromJS([
{
comment: 'ccc',
who: 'c1',
buttonInfo: ['a', 'b'],
},
{
comment: 'ddd',
who: 'd2',
buttonInfo: ['a''],
},
]);
This is working:
a.concat(b)
But this is not working:
[...a ,...b]
// or
b.map(v => {
a.push(v);
})

you can use concat method as it said in doc:
const list1 = List([ 1, 2, 3 ]);
const list2 = List([ 4, 5, 6 ]);
const array = [ 7, 8, 9 ];
const list3 = list1.concat(list2, array);
// List [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

An ImmutableJS list has a method named concat whose behavior is the same as a normal javascript array. However, you cannot use spread syntax for an Immutable array.
Also the syntax for push is different from the normal array, push like concat with Immutable List returns a new list, your map method will look like
b.map(v => {
a = a.push(v);
})
P.S. Using the above method though will mutate your array a. You must create a new List and then push both the array contents into it if you want to use push. However concat is the best way for your case

For add List to List in Immutable.js, you can use merge method.
Example:
const a = fromJS(
[
{
comment: 'aaaa',
who: 'a1',
buttonInfo: ['a', 'b', 'c'],
},
{
comment: 'bb',
who: 'a2',
buttonInfo: ['a', 'b', 'c'],
},
]
);
const b = fromJS(
[
{
comment: 'ccc',
who: 'c1',
buttonInfo: ['a', 'b'],
},
{
comment: 'ddd',
who: 'd2',
buttonInfo: ['a''],
},
]
);
a.merge(b);

How to find a value in object of objects with an array of keys

for example I have an object that that has objects and arrays in itself:
const object =
{
a: {
b: [
0: 'something',
1: {
c: 'the thing that I need',
},
],
},
};
and an array that has the keys as values:
const array =
[
'a', 'b', '1', 'c',
];
How can I use this array to navigate in the object and give me the value?
Maybe there is a way to do this with ramda? or just in general to make it look human readable.

You can reduce the array defining the path through the object.
You do have an error in the array. The path should be: [ 'a', 'b', '1', 'c' ], because the thing you need is inside the second element of the b array, not the first.
const object = {
a: {
b: [
'something',
{ c: 'the thing that I need' }
],
},
};
const path = [ 'a', 'b', '1', 'c' ];
const result = path.reduce(( source, next ) => source[ next ], object );
console.log( result );

Ian Hoffman-Hicks' superb crocks library has a function that does exactly that
import propPathOr from 'crocks/helpers/propPathOr'
const getC = propPathOr(null, ['a', 'b', '0', 'c'])
getC({ a: { b: [{ c: 'gotcha!' }] } }) === 'gotcha!' // true

This function is called path in Ramda.