given:
interface Dict {
[key: string]: any
}
const data: Dict[] = [
{ id: 'a' },
{ id: 'b', b: 'something' },
{ id: 'c', b: 'else' },
{ id: 'd', extra: 'hello world' },
{ id: 'e' },
];
where the keys of these Dict objects aren't specified...
How can I get this result?
const result = {
id: ['a', 'b', 'c', 'd', 'e'],
b: ['something', 'else'],
extra: ['hello world'],
// ... and any other possible key
}
You can flatten the object into a list of pairs, group it, and convert the pairs back to values:
const data = [
{ id: 'a' },
{ id: 'b', b: 'something' },
{ id: 'c', b: 'else' },
{ id: 'd', extra: 'hello world' },
{ id: 'e' },
];
let z = R.pipe(
R.chain(R.toPairs),
R.groupBy(R.head),
R.map(R.map(R.last))
)
console.log(z(data))
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>
Slight variation from Ori Drori answer:
(assuming that no properties in your objects are contained in arrays already)
const data = [
{ id: 'a' },
{ id: 'b', b: 'something' },
{ id: 'c', b: 'else' },
{ id: 'd', extra: 'hello world' },
{ id: 'e' }
];
const run = reduce(useWith(mergeWith(concat), [identity, map(of)]), {});
console.log(
run(data)
)
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.min.js"></script>
<script>const {reduce, useWith, mergeWith, concat, identity, map, of} = R;</script>
Use R.reduce with R.mergeWith and concat all items:
const { mergeWith, reduce } = R
const fn = reduce(mergeWith((a, b) => [].concat(a, b)), {})
const data = [
{ id: 'a' },
{ id: 'b', b: 'something' },
{ id: 'c', b: 'else' },
{ id: 'd', extra: 'hello world' },
{ id: 'e' },
];
const result = fn(data)
console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>
If you need the single value (extra) in array as well, map the items, and wrap with an array, just the values that are not an array already:
const { pipe, mergeWith, reduce, map, unless, is, of } = R
const fn = pipe(
reduce(mergeWith((a, b) => [].concat(a, b)), {}),
map(unless(is(Array), of))
)
const data = [
{ id: 'a' },
{ id: 'b', b: 'something' },
{ id: 'c', b: 'else' },
{ id: 'd', extra: 'hello world' },
{ id: 'e' },
];
const result = fn(data)
console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>
Related
I have object like this
[
{ A: '1' },
{ B: '2' },
{ C: '3' },
]
I want convert to like this
{
A: '1',
B: '2',
C: '3',
}
what is the best way to do it
Object.assign with spread syntax
let arr = [
{ A: '1' },
{ B: '2' },
{ C: '3' },
]
console.log(Object.assign(...arr));
let arr = [
{ A: '1' },
{ B: '2' },
{ C: '3' },
]
let output = {}
arr.map((obj) => {
output = {...output, ...obj}
})
console.log(output)
Object.assign and spread operator will do the trick :
let arrObject = [
{ A: "1" },
{ B: "2" },
{ C: "3" }
];
Object.assign(target, ...sources)
let obj = Object.assign({}, ...arrObject);
console.log(obj) => obj = { A: '1', B: '2', C: '3' }
Here is my simple array of objects
const array = [
{ name: 'a', val: '1234' },
{ name: 'b', val: '5678' },
{ name: 'c', val: '91011' },
{ name: 'c', val: '123536' },
{ name: 'e', val: '5248478' },
{ name: 'c', val: '5455' },
{ name: 'a', val: '548566' },
{ name: 'a', val: '54555' }
]
I need to group consecutive name elements and push the corresponding val. So the expected output should be
const array = [
{ name: 'a', vals: '1234' },
{ name: 'b', vals: '5678' },
{ name: 'c', vals: ['91011', '123536'] },
{ name: 'e', vals: '5248478' },
{ name: 'c', vals: '5455' },
{ name: 'a', vals: ['548566', '54555'] }
]
I tried it But could not get over it. Please help
const output = []
const result = array.reduce((a, c) => {
if (a.name === c.name) {
output.push(a);
}
}, []);
You were actually quite close:
const output = [];
array.reduce((a, c) => {
if (a.name === c.name) { // current element equals previous element, lets merge
a.values.push(c.val);
} else output.push(a = { name: c.name, values: [c.val] ); // otherwise add new entry
return a; // the current element is the next previous
} , {}); // start with an empty a, so that c always gets pushed
Note that it makes little sense to store numbers as string though.
You can reduce the array like this. Compare the current name with previous item's name. If they are not the same, add a new item to the accumulator. If they are the same, then use concat the merge val with the last item in accumulator. concat is used because vals could either be a string or an array.
const array = [
{ name: 'a', val: '1234' },
{ name: 'b', val: '5678' },
{ name: 'c', val: '91011' },
{ name: 'c', val: '123536' },
{ name: 'e', val: '5248478' },
{ name: 'c', val: '5455' },
{ name: 'a', val: '548566' },
{ name: 'a', val: '54555' }
]
const merged = array.reduce((acc, { name, val }, i, arr) => {
// check if name is same as the previous name
if (arr[i - 1] && arr[i - 1].name === name) {
const prev = acc[acc.length - 1]; // last item in the accumulator
prev.vals = [].concat(prev.vals, val)
} else
acc.push({ name, vals: val })
return acc
}, [])
console.log(merged)
I'm a bit stuck with something implying recursion. I am receiving data
from an API. It looks like this:
const input = [
{ id: 'a', level: 0 },
{ id: 'b', level: 1 },
{ id: 'c', level: 1 },
{ id: 'd', level: 2 },
{ id: 'e', level: 1 },
{ id: 'f', level: 0 },
];
and I need something like
const out = [
{ id: 'a', nodes: [
{ id: 'b', nodes: [] },
{ id: 'c', nodes: [
{ id: 'd', nodes: [] },
] },
{ id: 'e', nodes: [] },
] },
{ id: 'f', nodes: [] },
];
How would you achieve that in an elegant way such as out = f(input) ?
I feel we can do a recursive nest method through a reduce but I did not manage to get it right :)
Thanks in advance!
You could use a helper array for the levels with the latest array/nodes property from the object.
const
input = [{ id: 'a', level: 0 }, { id: 'b', level: 1 }, { id: 'c', level: 1 }, { id: 'd', level: 2 }, { id: 'e', level: 1 }, { id: 'f', level: 0 }],
result = [],
levels = [result];
input.forEach(({ id, level }) =>
levels[level].push({ id, nodes: levels[level + 1] = [] })
);
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }
You may try out like,
function makeObject(id){
return { id: id, nodes:[] };
}
function addObjectToNodes(array, id, node){
array.map(a => {
if(a.id === id)
a.nodes.push(node);
});
}
const nodes = [];
nodes.push(makeObject('a'));
nodes.push(makeObject('f'));
addObjectToNodes(nodes, 'a', makeObject('b'));
addObjectToNodes(nodes, 'a', makeObject('c'));
addObjectToNodes(nodes, 'a', makeObject('d'));
addObjectToNodes(nodes, 'a', makeObject('e'));
console.log(nodes);
const r = ['a', 'b', 'c', 'l', 'p'];
const arr = [{
name: "ss3",
id: 'c'
}, {
name: "ss2",
id: 'b'
}, {
name: "ss4",
id: 'p'
}, {
name: "ss1",
id: 'a'
}]
var newArray =arr.map((i)=>{
let e = r[i];
if(i.id===e){
return i
}
})
console.log(newArray)
Expected output
const arr = [{
name: "ss1",
id: 'a'
}, {
name: "ss2",
id: 'b'
}, {
name: "ss3",
id: 'c'
}, {
name: "ss4",
id: 'p'
}
]
Given two arrays r and arr, I wish to sort arr with respect to r, i.e. in alphabetical order by id.
https://jsbin.com/yitijiboso/edit?html,js,output
I think this might be a concise (although not very performant) way to achieve the desired output:
const arr1 = ['a', 'b', 'c', 'l', 'p'];
const arr2 = [
{
name: "ss3",
id: 'c'
},
{
name: "ss2",
id: 'b'
}, {
name: "ss4",
id: 'p'
},
{
name: "ss1",
id: 'a'
}
];
arr2.sort((a, b) => arr1.indexOf(a.id) - arr1.indexOf(b.id));
console.log(arr2);
Easy:
make a map from main 'arr' keyBy 'id' https://www.npmjs.com/package/lodash.keyby
loop across 'r', if key exist in new map, get value and push to new array
const arrMap = _.keyBy(arr, 'id');
let newR = [];
r.forEach( key => {
if ( arrMap[key] ) {
newR.push( arrMap[key] );
}
} );
console.log( 'new array', newR );
Taking a clue from #Petr Broz, here's my suggestion:
const r = ['a', 'b', 'c', 'l', 'p'];
const arr = [
{
name: "ss3",
id: 'c'
},
{
name: "ss2",
id: 'b'
}, {
name: "ss4",
id: 'p'
},
{
name: "ss1",
id: 'a'
}
];
arr.sort((a, b) => r.indexOf(a.id) > r.indexOf(b.id));
console.log(arr);
Main difference is that this code utilizes the arrays as named by the OP and uses a greater than comparison operator. However, if you just want to have the array arr sorted in alphabetical order you don't need to compare it with array r:
const arr = [
{
name: "ss3",
id: 'c'
},
{
name: "ss2",
id: 'b'
}, {
name: "ss4",
id: 'p'
},
{
name: "ss1",
id: 'a'
}
];
arr.sort(function(a, b)
{
if (a.id > b.id) {
return 1;
}
else
if (a.id < b.id) {
return -1;
}
else
{
return 0;
}
});
console.log(arr);
Note, in this example the return values are numeric instead of boolean values which would be helpful if the array to be sorted were to have duplicate values.
I try to write insert into a tree data structure recursively in javascript with tree-node, but don't get it working.
So my question would be, how to approach the issue.
this is my data:
[ { id: 'a', children: [ 'b', 'c' ] },
{ id: 'b', children: [ '' ] },
{ id: 'c', children: [ 'b', 'd' ] },
{ id: 'd', children: [ 'b' ] } ]
I want that showing up in a tree like the following:
a
/\
b c
/\
b d
\
b
Edit: Added code
I Thought i could do something like this, but that doesn't work... and of course has high complexity because of the nested forEach:
var Node = require("tree-node");
var testarray =
[
{ id: 'a', children: [ 'b', 'c' ] },
{ id: 'b', children: [ '' ] },
{ id: 'c', children: [ 'b', 'd' ] },
{ id: 'd', children: [ 'b' ] }
]
function appendChildRecursive(parent) {
var childnode = new Node()
var data = parent.data("children")
testarray.forEach(function(item){
if(data !== undefined) {
data.forEach(function (child) {
if (item.id == child) {
childnode.data("id", child).data("children", item.children)
childnode = appendChildRecursive(childnode)
parent.appendChild(childnode)
}
})
}
})
return parent
}
var root = new Node();
root.data("id",testarray[0].id).data("children",testarray[0].children)
root=appendChildRecursive(root)
You could use a hash table for the last inserted nodes and keep the reference to the last nodes by overwriting the reference.
var data = [{ id: 'a', children: ['b', 'c'] }, { id: 'b', children: [] }, { id: 'c', children: ['b', 'd'] }, { id: 'd', children: ['b'] }],
tree = function (array) {
var nodes = Object.create(null),
r = {};
array.forEach(function (a) {
if (!nodes[a.id]) {
nodes[a.id] = { id: a.id, children: [] };
r = nodes[a.id];
}
a.children.forEach(function (b) {
nodes[b] = { id: b, children: [] };
nodes[a.id].children.push(nodes[b]);
});
});
return r;
}(data);
console.log(tree);
.as-console-wrapper { max-height: 100% !important; top: 0; }
Your data structure is wrong.
Each 'leaf' should contain reference to the 'left' and 'right' element.
for example:
const first = { id: 'a', left: null, right: null };
const second = { id: 'b', left: null, right: first };
// etc...
The children approach would be more suitable for graph.
But you still have to store references, not ids.