Related
Array of dictionaries should be converted simpler form.
data = [{A:1},{B:2},{C:3}]
data = {A: 1, B: 2}
data = ["0":{ A : 1, B : 2 , C : 3}]
Both are completely different datasets. I'm trying to map it also like below format.
The above should become like
data = [
{
name: "A",
y: 1
},
{
name: "B",
y: 2
},
{
name: "C",
y: 3
}
];
I tried this following approach but it's wrong
name = {}
data.forEach(function(k,x){
return name['name'] = k , name["y"] = x
})
Please suggest me a better approach.
map each object's entries to extract the key and the value, and return an object with name and y keys:
const data = [{A:1},{B:2},{C:3}]
const output = data.map(item => {
const [name, y] = Object.entries(item)[0];
return { name, y };
});
console.log(output);
If the keys (A, B, etc) are guaranteed to be unique throughout the array, then everything becomes simpler.
const data = [{A:1},{B:2},{C:3}];
const merged = Object.assign({}, ...data);
const newData = Object.entries(merged)
.map(([name, y]) => ({ name, y }));
console.log(newData);
However, if the keys aren't guaranteed unique, then refer to CertainPerformance's answer.
you can implement like this
var data = [{A:1},{B:2},{C:3}];
var reformattedArra = data.map(obj => {
let val = {};
val.name = Object.keys(obj)[0];
val.y = obj[Object.keys(obj)[0]];
return val;
})
console.log(JSON.stringify(reformattedArra));
I would say, use Object.keys() which is widly supported
let data = [{A:1},{B:2},{C:3}];
data = Object.assign({}, ...data);
data = Object.keys(data).map(key => ({ name: key, y: data[key] }));
console.log(data);
You yould could chekc the data format and if it is not an array, build one and reduce the array by taking the objetcs and create for each key/value a new object for the result set.
function simple(data) {
return (Array.isArray(data) ? data : [data]).reduce((r, o) => [...r, ...Object.entries(o).map(([name, y]) => ({ name, y }))], []);
}
console.log(simple([{ A: 1 }, { B: 2 }, { C: 3, D: 4 }]));
console.log(simple({ A: 1, B: 2 }));
.as-console-wrapper { max-height: 100% !important; top: 0; }
I have an array of objects in the format
{type: number, sub_type: number}
I need to sort them into an array of objects formatted like this
{
type_id: (type from at least one object in array above),
sub_types: [
(all sub types from objects in array above that match this type)
]
}
This is what I came up but I think there is a more efficient way. rawTypes is an array of objects in need of formatting, types ends up being the array of formatted objects.
const typeIds = [...new Set(rawTypes.map(val => val.type))];
const types = typeIds.map(val => ({type_id: val, sub_types: [] }));
rawTypes.forEach(obj => {
let typeIndex = types.reduce((accum, val, i) => val.type_id === obj.type ? i : accum, 0);
types[typeIndex].sub_types.push(obj.sub_type);
});
I think a better solution would use recursion but I can't think of how to do it.
Look at this approach
var data = [{type: 5, sub_type: 10}, {type: 5, sub_type: 11}, {type: 6, sub_type: 12}];
var obj = data.reduce((a, c) => {
var current = a[`type_id_${c.type}`];
if (current) {
current.sub_types.push(c.sub_type);
} else {
var key = `type_id_${c.type}`;
a = { ...a, ...{ [key]: {sub_types: [c.sub_type], 'key': c.type} } };
}
return a;
}, {});
var array = Object.keys(obj).map((k) => ({ 'type': obj[k].key, 'subtypes': obj[k].sub_types }));
console.log(array)
.as-console-wrapper {
max-height: 100% !important
}
I have two array object as following:
var arr1 = [
{
name: 1,
value: 10
},
{
name: 2,
value: 15
}
]
var arr2 = [
{
name: 3,
value: 5
},
{
name: 4,
value: 3
}
]
I want to redefine the key and reduce each data with the same index.
output:
var arr1 = [
{
itemLabel: 1,
itemValue: 5
},
{
itemLabel: 2,
itemValue: 12
}
]
I'm doing now as following:
formatData = arr1.map((row, index) => ({
itemLabel: arr1.name,
itemValue: arr1.value - arr2[index].value
}))
Is there any better solution of doing this?
One-man army
A simple recursive program that handles everything in a single function. There's a clear mixture of concerns here which hurts of function's overall readability. We'll see one such remedy for this problem below
const main = ([x, ...xs], [y, ...ys]) =>
x === undefined || y === undefined
? []
: [ { itemLabel: x.name, itemValue: x.value - y.value } ] .concat (main (xs, ys))
const arr1 =
[ { name: 1, value: 10 }, { name: 2, value: 15 } ]
const arr2 =
[ { name: 3, value: 5 }, { name: 4, value: 3 } ]
console.log (main (arr1, arr2))
// [ { itemLabel: 1, itemValue: 5 },
// { itemLabel: 2, itemValue: 12 } ]
Thinking with types
This part of the answer is influenced by type theory from the Monoid category – I won't go too far into it because I think the code should be able to demonstrate itself.
So we have two types in our problem: We'll call them Foo and Bar
Foo – has name, and value fields
Bar – has itemLabel and itemValue fields
We can represent our "types" however we want, but I chose a simple function which constructs an object
const Foo = (name, value) =>
({ name
, value
})
const Bar = (itemLabel, itemValue) =>
({ itemLabel
, itemValue
})
Making values of a type
To construct new values of our type, we just apply our functions to the field values
const arr1 =
[ Foo (1, 10), Foo (2, 15) ]
const arr2 =
[ Foo (3, 5), Foo (4, 3) ]
Let's see the data we have so far
console.log (arr1)
// [ { name: 1, value: 10 },
// { name: 2, value: 15 } ]
console.log (arr2)
// [ { name: 3, value: 5 },
// { name: 4, value: 3 } ]
Some high-level planning
We're off to a great start. We have two arrays of Foo values. Our objective is to work through the two arrays by taking one Foo value from each array, combining them (more on this later), and then moving onto the next pair
const zip = ([ x, ...xs ], [ y, ...ys ]) =>
x === undefined || y === undefined
? []
: [ [ x, y ] ] .concat (zip (xs, ys))
console.log (zip (arr1, arr2))
// [ [ { name: 1, value: 10 },
// { name: 3, value: 5 } ],
// [ { name: 2, value: 15 },
// { name: 4, value: 3 } ] ]
Combining values: concat
With the Foo values properly grouped together, we can now focus more on what that combining process is. Here, I'm going to define a generic concat and then implement it on our Foo type
// generic concat
const concat = (m1, m2) =>
m1.concat (m2)
const Foo = (name, value) =>
({ name
, value
, concat: ({name:_, value:value2}) =>
// keep the name from the first, subtract value2 from value
Foo (name, value - value2)
})
console.log (concat (Foo (1, 10), Foo (3, 5)))
// { name: 1, value: 5, concat: [Function] }
Does concat sound familiar? Array and String are also Monoid types!
concat ([ 1, 2 ], [ 3, 4 ])
// [ 1, 2, 3, 4 ]
concat ('foo', 'bar')
// 'foobar'
Higher-order functions
So now we have a way to combine two Foo values together. The name of the first Foo is kept, and the value properties are subtracted. Now we apply this to each pair in our "zipped" result. Functional programmers love higher-order functions, so you'll appreciate this higher-order harmony
const apply = f => xs =>
f (...xs)
zip (arr1, arr2) .map (apply (concat))
// [ { name: 1, value: 5, concat: [Function] },
// { name: 2, value: 12, concat: [Function] } ]
Transforming types
So now we have the Foo values with the correct name and value values, but we want our final answer to be Bar values. A specialized constructor is all we need
Bar.fromFoo = ({ name, value }) =>
Bar (name, value)
Bar.fromFoo (Foo (1,2))
// { itemLabel: 1, itemValue: 2 }
zip (arr1, arr2)
.map (apply (concat))
.map (Bar.fromFoo)
// [ { itemLabel: 1, itemValue: 5 },
// { itemLabel: 2, itemValue: 12 } ]
Hard work pays off
A beautiful, pure functional expression. Our program reads very nicely; flow and transformation of the data is easy to follow thanks to the declarative style.
// main :: ([Foo], [Foo]) -> [Bar]
const main = (xs, ys) =>
zip (xs, ys)
.map (apply (concat))
.map (Bar.fromFoo)
And a complete code demo, of course
const Foo = (name, value) =>
({ name
, value
, concat: ({name:_, value:value2}) =>
Foo (name, value - value2)
})
const Bar = (itemLabel, itemValue) =>
({ itemLabel
, itemValue
})
Bar.fromFoo = ({ name, value }) =>
Bar (name, value)
const concat = (m1, m2) =>
m1.concat (m2)
const apply = f => xs =>
f (...xs)
const zip = ([ x, ...xs ], [ y, ...ys ]) =>
x === undefined || y === undefined
? []
: [ [ x, y ] ] .concat (zip (xs, ys))
const main = (xs, ys) =>
zip (xs, ys)
.map (apply (concat))
.map (Bar.fromFoo)
const arr1 =
[ Foo (1, 10), Foo (2, 15) ]
const arr2 =
[ Foo (3, 5), Foo (4, 3) ]
console.log (main (arr1, arr2))
// [ { itemLabel: 1, itemValue: 5 },
// { itemLabel: 2, itemValue: 12 } ]
Remarks
Our program above is implemented with a .map-.map chain which means handling and creating intermediate values multiple times. We also created an intermediate array of [[x1,y1], [x2,y2], ...] in our call to zip. Category theory gives us things like equational reasoning so we could replace m.map(f).map(g) with m.map(compose(f,g)) and achieve the same result. So there's room to improve this yet, but I think this is just enough to cut your teeth and start thinking about things in a different way.
Your code is just fine, you could use recursion as well:
var arr1 =[{
name: 1,
value: 10
}, {
name: 2,
value: 15
}];
var arr2= [{
name: 3,
value: 5
}, {
name: 4,
value: 3
}]
const createObject=(arr1,arr2,ret=[])=>{
if(arr1.length!==arr2.length){
throw("Arrays should be the same length.")
}
const item = {
itemLabel: arr1[0].name,
itemValue: arr1[0].value - arr2[0].value
};
if(arr1.length===0){
return ret;
};
return createObject(arr1.slice(1),arr2.slice(1),ret.concat(item));
}
console.log(createObject(arr1,arr2));
Both functions implementing a map or reduce would have to use either arr1 or arr2 outside of their scope (not passed to it as parameter) so strictly speaking not pure. But you could easily solve it with partial application:
var arr1 =[{
name: 1,
value: 10
}, {
name: 2,
value: 15
}];
var arr2= [{
name: 3,
value: 5
}, {
name: 4,
value: 3
}];
const mapFunction = arr2 => (item,index) => {
return {
itemLabel: item.name,
itemValue: item.value - arr2[index].value
}
}
var createObject=(arr1,arr2,ret=[])=>{
if(arr1.length!==arr2.length){
throw("Arrays should be the same length.")
}
const mf = mapFunction(arr2);
return arr1.map(mf);
}
console.log(createObject(arr1,arr2));
But as CodingIntrigue mentioned in the comment: none of these are any "better" than you've already done.
To make your solution more functional you need to change your anonymous function to a pure (anonymous) function.
A pure function is a function that, given the same input, will always return the same output
The anonymous function depends on the mutable variable arr1 and arr2. That means that it depends on the system state. So it doesn't fit into the pure function rule.
The following is maybe not the best implementaion but I hope it gives you an idea..
Let's Make it Pure
To make it pure we can pass the variables into the function as arguments
const mapWithObject = (obj2, obj1, index) => ({
itemLabel: obj1.name,
itemValue: obj1.value - obj2[index].value
})
// example call
const result = mapWithObject(arr2, arr1[0], 0)
Ok, but now the function doesn't fit into map anymore because it takes 3 arguments instead of 2..
Let's Curry it
const mapWithObject = obj2 => (obj1, index) => ({
itemLabel: obj1.name,
itemValue: obj1.value - obj2[index].value
})
const mapObject_with_arr2 = mapWithObject(arr2)
// example call
const result = mapObject_with_arr2(arr1[0], 0)
Full Code
const arr1 = [{
name: 1,
value: 10
},
{
name: 2,
value: 15
}
]
const arr2 = [{
name: 3,
value: 5
},
{
name: 4,
value: 3
}
]
const mapWithObject = obj2 => (obj1, index) => ({
itemLabel: obj1.name,
itemValue: obj1.value - obj2[index].value
})
const mapObject_with_arr2 = mapWithObject(arr2)
const mappedObject = arr1.map(mapObject_with_arr2)
console.log(mappedObject)
If you don't care to much about performance, but want to separate your concerns a bit further you could use this approach:
Define a function that does the "pairing" between arr1 and arr2
[a, b, c] + [1, 2, 3] -> [ [ a, 1 ], [ b, 2 ], [ c, 3 ] ]
Define a function that clearly shows the merge strategy of two objects
{ a: 1, b: 10 } + { a: 2, b: 20 } -> { a: 1, b: -10 }
Define simple helpers that compose the two so you can pass your original arrays and be returned the desired output in one function call.
Here's an example:
var arr1=[{name:1,value:10},{name:2,value:15}],arr2=[{name:3,value:5},{name:4,value:3}];
// This is a very general method that bundles two
// arrays in an array of pairs. Put it in your utils
// and you can use it everywhere
const pairs = (arr1, arr2) => Array.from(
{ length: Math.max(arr1.length, arr2.length) },
(_, i) => [ arr1[i], arr2[i] ]
);
// This defines our merge strategy for two objects.
// Ideally, you should give it a better name, based
// on what the objects represent
const merge =
(base, ext) => ({
itemLabel: base.name,
itemValue: base.value - ext.value
});
// This is a helper that "applies" our merge method
// to an array of two items.
const mergePair = ([ base, ext ]) => merge(base, ext);
// Another helper that composes `pairs` and `mergePair`
// to allow you to pass your original data.
const mergeArrays = (arr1, arr2) => pairs(arr1, arr2).map(mergePair);
console.log(mergeArrays(arr1, arr2));
Would like to merge an array of objects resulting in an object of unique keys and array of values (duplication of values is ok). Solutions in vanilla JS or lodash preferred.
eg - from this:
[{
a: 1,
b: 2
}, {
a: 1,
c: 3
}]
to this:
{
a: [1, 1],
b: [2],
c: [3]
}
You can use _.mergeWith() with the spread syntax to combine the objects:
const data = [{"a":1,"b":2},{"a":1,"c":3}];
const result = _.mergeWith({}, ...data, (v1 = [], v2) => [...v1, v2]);
console.log(result);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>
ES6 variant:
const a = [{
a: 1,
b: 2
}, {
a: 1,
c: 3
}]
const b = a.reduce((acc, cur) => Object.assign(acc,
...Object.keys(cur).map(key => ({ [key]: (acc[key] || []).concat(cur[key]) })))
, {})
console.log(b)
without loadash:
var t = [{
a: 1,
b: 2
}, {
a: 1,
c: 3
}];
var result = {};
debugger;
for(var i=0; i<t.length; i++){
for(var j in t[i]){
if(result.hasOwnProperty(j)){
result[j].push(t[i][j]);
}else{
result[j] = [t[i][j]];
}
}
}
console.log(result);
A quick search here in stack reveals that #elclanrs already wrote code for that here However based on the comments, it needs a little tweaking to accept an array of objects, so I added a bit of change to the original code itself.
so basically it boils to the function call:
var merge = function() {
return [].reduce.call(arguments, function(acc, x) {
for(i=0;i<x.length;i++){
Object.keys(x[i]).forEach(function(k) {
acc[k] = (acc[k]||[]).concat([x[i][k]])
});
}
return acc
},{})
}
}
Here's a snippet using the function call (with a bit of small change I put) in that post:
var x = [{a: 1, b: 2}, {a: 1,c: 3}]
var merge = function() {
return [].reduce.call(arguments, function(acc, x) {
for(i=0;i<x.length;i++){
Object.keys(x[i]).forEach(function(k) {
acc[k] = (acc[k]||[]).concat([x[i][k]])
});
}
return acc
},{})
}
y = merge(x);
alert(JSON.stringify(y));
You can use lodash#mergeWith wrapped in a lodash#spread to make lodash#mergeWith treat an array as a list of arguments. We use lodash#concat as a supporting function to concatenate an empty object (to avoid mutating the objects in the collection), the collection, and the customizer function that merges the entire collection. The customizer is composed using lodash#flow, wherein its first argument is lodash#concat that only accepts an arity of 2 using lodash#ary and the second argument uses lodash#compact -- It removes all undefined values in an array.
var result = _.spread(_.mergeWith)(
_.concat({}, data, _.flow(_.ary(_.concat, 2), _.compact))
);
var data = [{
"a": 1,
"b": 2
}, {
"a": 1,
"c": 3
}];
var result = _.spread(_.mergeWith)(
_.concat({}, data, _.flow(_.ary(_.concat, 2), _.compact))
);
console.log(result);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>
I have two arrays of objects:
Array1:
var myArr1 = [];
myArr1["1"]={any:1,some:1};
myArr1["2"]={any:2,some:2};
myArr1["3"]={any:3,some:3};
Array2:
var myArr2 = [];
myArr2["1"]={other:1};
myArr2["2"]={other:2};
And I want them to be merged by their keys into a new Attribute, so the result will be:
[
{any:1,some:1,myNewAttribute:{other:1}},
{any:2,some:2,myNewAttribute:{other:2}},
{any:3,some:3,myNewAttribute:{other:3}}
]
I tried to achieve it with lodash's _.merge() but I failed miserably. _.merge only adds the second array after the first, but does not match their keys / ids.
You could map the second array to a new property and merge later.
With lodash
var data1 = [{ any: 1, some: 1 }, { any: 2, some: 2 }, { any: 3, some: 3 }],
data2 = [{ other: 1 }, { other: 2 }, { other: 3 }];
console.log(_.merge(data1, _.map(data2, x => ({ myNewAttribute: x }))));
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>
With ES6, without lodash
var data1 = [{ any: 1, some: 1 }, { any: 2, some: 2 }, { any: 3, some: 3 }],
data2 = [{ other: 1 }, { other: 2 }, { other: 3 }];
console.log(data1.map((a, i) => Object.assign({}, a, { myNewAttribute: data2[i] })));
You don't need lodash:
myArr1.map((e1, idx) => Object.assign({}, e1, {myNewAttribute: myArr2[idx]}))
You could get fancy and write a little function called map2, which takes two arrays, and invokes a callback with the two elements:
function map2(a1, a2, fn) {
return a1.map((elt, idx) => fn(elt, a2[idx]);
}
Now you can write the solution as
map2(myArr1, myArr2, (e1, e2) => Object.assign({}, e1, {myNewAttribute: e2}))
From the perspective of program design, what we are doing here is "separating concerns". The first concern is the abstract operation of looping over two arrays in parallel and doing something with each pair of elements. That is what is represented by map2. The second concern is the specific way you want to combine the elements. That is what is represented by the function we are passing to map2. This could be made clearer and somewhat self-documenting by writing it separately:
function combineObjects(e1, e2) {
return Object.assign({}, e1, {myNewAttribute: e2});
}
map2(myArr1, myArr2, combineObjects);
Of course, in the real world, you'd want to handle the case where the two arrays were of different length, pass an index to the callback as a third parameter for use if necessary, support a third thisArg-type parameter analogous to map, etc.
You can do like this:
var first = [{any:1,some:1},{any:2,some:2},{any:3,some:3}];
var second = [{other:1},{other:2},{other:3}];
for(var i = 0; i < first.length; i++){
if(first[i] && second[i]){
first[i]['mycustomitem'] = second[i];
}
}
console.log(first);
In order to prove, what I did comment 30 minutes ago -
How to merge two dictionaries in javascript -
there is a possible reduce approach ...
... firstly provided as lodash based example ...
var
myArr1 = [
{any: 1, some: 1},
{any: 2, some: 2},
{any: 3, some: 3}
],
myArr2 = [
{other: 1},
{other: 2}
],
mergedObjectList = _.reduce(myArr1, function (collector, item_1, idx) {
var
item_2 = collector[idx],
merger = _.assign({}, item_1, item_2);
// or whatever one wants to do to `merger` with `myNewAttribute`
collector[idx] = merger;
return collector;
}, _.clone(myArr2));
console.log("myArr1 : ", myArr1);
console.log("myArr2 : ", myArr2);
console.log("mergedObjectList : ", mergedObjectList);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>
... and secondly as language core only based example ...
var
myArr1 = [
{any: 1, some: 1},
{any: 2, some: 2},
{any: 3, some: 3}
],
myArr2 = [
{other: 1},
{other: 2}
],
mergedObjectList = myArr1.reduce(function (collector, item_1, idx) {
var
item_2 = collector[idx],
merger = Object.assign({}, item_1, item_2);
// or whatever one wants to do to `merger` with `myNewAttribute`
collector[idx] = merger;
return collector;
}, Array.from(myArr2));
console.log("myArr1 : ", myArr1);
console.log("myArr2 : ", myArr2);
console.log("mergedObjectList : ", mergedObjectList);
Try this function:
function mergeDictionary(_dctn1,_dctn2)
{
var newDict = [];
for(var i in _dctn1)
{
newDict[i] = _dctn1[i];
}
for(var j in _dctn2)
{
if(newDict[j] == undefined)
{
newDict[j] = _dctn2[j];
}
else
{
for(var k in _dctn2[j])
{
newDict[j][k] = _dctn2[j][k];
}
}
}
return newDict;
}
var myArr1 = [];
myArr1["1"]={any:1,some:1};
myArr1["2"]={any:2,some:2};
myArr1["3"]={any:3,some:3};
var myArr2 = [];
myArr2["1"]={other:1};
myArr2["2"]={other:2};
console.log(mergeDictionary(myArr1, myArr2));