I have to calculate a sum of certain object values ( not all )
I have this object :
let object = {a: 1, b: 4, c: 2, d: 3, e: 10}
I need to sum just the a, c, d, e values.
Actually I use this method which sums all the values and gives me 20, but I need to have 16.
Object.keys(object).reduce((sum, key) => sum + parseFloat(object[key] || 0), 0)
How can I do this sum ?
Your sum function is good as it is, you just need to apply a filter
Object.keys(object)
.filter(key => key !== 'b')
.reduce((sum, key) => sum + parseFloat(object[key] || 0), 0)
Or, if you want a whitelist
const validKeys = {
a: true,
b: false, // optional
c: true,
d: true,
e: true
}
Object.keys(object)
.filter(key => validKeys[key])
.reduce((sum, key) => sum + parseFloat(object[key] || 0), 0)
To follow what you originally did, You should have an array of the keys and check to see if it is included before you add it.
const myObject = {a: 1, b: 4, c: 2, d: 3, e: 10}
const keys = ['a', 'c','d', 'e']
const entries = Object.entries(myObject)
const result = entries.reduce( (total, [key, value]) => (keys.includes(key) ? value : 0) + total, 0)
console.log(result)
smarter way is to loop over the keys
const myObject = {a: 1, b: 4, c: 2, d: 3, e: 10}
const keys = ['a', 'c','d', 'e']
const result = keys.reduce( (total, key) => (myObject[key] || 0) + total, 0)
console.log(result)
I'll add my two cents to the thread for...in is awesome too xD
let object = {a: 1, b: 4, c: 2, d: 3, e: 10}
let sum = 0;
const keys = ['a', 'c', 'd', 'e'];
for(let key in object) {
if(keys.includes(key)) //or key === 'a' || key === 'c' ..
sum += object[key];
}
console.log(sum);
You could take the wanted keys directly.
let object = {a: 1, b: 4, c: 2, d: 3, e: 10},
keys = ['a', 'c', 'd', 'e'],
result = keys.reduce((sum, key) => sum + (object[key] || 0), 0);
console.log(result);
You could either declare the keys you want to sum (whitelist) or those you wish to omit (blacklist). I've used the latter approach here:
let object = {a: 1, b: 4, c: 2, d: 3, e: 10},
ignore = ['b'],
sum = Object.keys(object)
.filter(key => !ignore.includes(key))
.reduce((total, key) => total += object[key], 0);
console.log(sum); //16
Fiddle
Related
If x = {a: 4, b:5, c:6, d:7} and y = {a: true, d: true}
I want to produce {a: 4, d: 7}
Note that the object y will only ever contain the fields that are to be included and the values of y will always be true (otherwise the key will not exist in the first place.
This is what I have, its a good solution (I think) but was wondering if there is anything simpler and maybe using the spread syntax ...
const changedFields = Object.keys(y).reduce((acc, key) => {
acc[key] = x[key];
return acc;
}, {});
Your .reduce looks fine. Another option is to map the keys in y to an array of entries.
const x = {a: 4, b:5, c:6, d:7};
const y = {a: true, d: true};
const output = Object.fromEntries(
Object.keys(y).map(key => [key, x[key]])
);
console.log(output);
You can use Object.entries and filter
const x = {
a: 4,
b: 5,
c: 6,
d: 7
}
const y = {
a: true,
d: true
}
const result = Object.fromEntries(Object.entries(x).filter(([key]) => {
return y[key]
}))
console.log(result)
Other option is to use reduce
const x = {
a: 4,
b: 5,
c: 6,
d: 7
}
const y = {
a: true,
d: true
}
const result = Object.keys(y).reduce((acc, key) => ({
...acc,
[key]: x[key]
}), {})
console.log(result)
also u can use reduce and hasOwnProperty
const x = {a: 4, b:5, c:6, d:7}
const y = {a: true, d: true}
const res = Object.entries(x).reduce((prev, [key, value]) => {
if (y.hasOwnProperty(key)) {
prev[key] = value
}
return prev
}, {})
console.log(res)
Sometimes, simplest solution can be going back to for..in
const x = {a: 4, b:5, c:6, d:7};
const y = {a: true, d: true};
const changedFields = {}
for (let key in y) {
changedFields[key] = x[key]
}
console.log(changedFields)
Say I have the following array:
let arr = [{a: 1, b: 2}, {a: 2, b: 4}, {a: 8, b: -1}]
I would like to compute the cumulative sum of each key, but I would also like the output to be an array of the same length with the cumulative values at each step. The final result should be:
[{a: 1, b: 2}, {a: 3, b: 6}, {a: 11, b: 5}]
My issue is that I am not able to obtain the array as desired. I only get the final object with this:
let result = arr.reduce((accumulator, element) => {
if(accumulator.length === 0) {
accumulator = element
} else {
for(let i in element){
accumulator[i] = accumulator[i] + element[i]
}
}
return accumulator
}, [])
console.log(result); // {a: 11, b: 5}
What you're after sounds like the scan() higher-order function (borrowing the idea from ramda.js), which allows you to return an accumulated result for each element within your array. The scan method is similar to how the .reduce() method behaves, except that it returns the accumulator for each element. You can build the scan() function yourself like so:
let arr = [{a: 1, b: 2}, {a: 2, b: 4}, {a: 8, b: -1}];
const scan = ([x, ...xs], fn) => xs.reduce((acc, elem) => {
return [...acc, fn(acc.at(-1), elem)];
}, xs.length ? [x] : []);
const res = scan(arr, (x, y) => ({a: x.a+y.a, b: x.b+y.b}));
console.log(res);
You might consider further improvements such as providing an initial value to the scan method (similar to how reduce accepts one). Also, if you need better browser support the .at() method currently has limited browser support, so you may instead consider creating your own at() function:
const at = (arr, idx) => idx >= 0 ? arr[idx] : arr[arr.length + idx];
You can easily achieve the result using reduce as
let arr = [
{ a: 1, b: 2 },
{ a: 2, b: 4 },
{ a: 8, b: -1 },
];
const result = arr.reduce((acc, curr, i) => {
if (i === 0) acc.push(curr);
else {
const last = acc[i - 1];
const newObj = {};
Object.keys(curr).forEach((k) => (newObj[k] = curr[k] + last[k]));
acc.push(newObj);
}
return acc;
}, []);
console.log(result);
Something like this:
const arr = [{a: 1, b: 2}, {a: 2, b: 4}, {a: 8, b: -1}]
const result = arr.reduce((accumulator, element, index) => {
if(accumulator.length === 0) {
accumulator.push(element)
} else {
const sum = {};
for(let i in element) {
sum[i] = element[i] + (accumulator[index - 1][i] || 0)
}
accumulator.push(sum)
}
return accumulator
}, [])
console.log(result);
Another option is keep sum result using a Map, it helps if keys in elements of the array are not always same.
const arr = [{a: 1, b: 2}, {a: 2}, {a: 8, b: -1}];
const map = new Map();
const result = arr.map((element) => {
const sum = {};
for (let i in element) {
sum[i]= element[i] + (map.get(i) || 0);
map.set(i, sum[i]);
}
return sum;
});
console.log(result);
Here is a bit more concise reduce, probably not as readable as a consequence...
array.reduce((y,x,i) => ( i===0 ? y : [...y, {a: x.a + y[i-1].a, b: x.b + y[i-1].b}]),[array[0]])
let array = [{a: 1, b: 2}, {a: 2, b: 4}, {a: 8, b: -1}]
let culm = array.reduce((y,x,i) => ( i===0 ? y : [...y, {a: x.a + y[i-1].a, b: x.b + y[i-1].b}]),[array[0]])
console.log(culm)
Given:
const xs =
[ {a: 1, b: 2}
, {a: 2, b: 4}
, {a: 8, b: -1}];
Define a function sum such as:
const sum = ([head, ...tail]) =>
tail.reduce((x, y) =>
({a: (x.a+y.a), b: (x.b+y.b)}), head);
sum(xs);
//=> {a: 11, b: 5}
Then apply that function in a map on larger slices of xs:
xs.map((_, i, arr) => sum(arr.slice(0, i+1)));
//=> [ {a: 1, b: 2}
//=> , {a: 3, b: 6}
//=> , {a: 11, b: 5}]
Sorry, in advance if the title is unclear, but it's hard to describe it in a words.
What I have:
const obj = {
a: 5,
b: 3,
c: 0,
d: 9
}
What I want to have:
const arr = [[a, 5] ,[b, 3]]
Basically, I try to write a function that return me array of entries, but it has too meet requirements:
don't want objects when values is equal to 0
sum of values must be less than 10
First point is easy for me and I can do it by
Object.entries(obj).filter(([k, v])=> v !== 0)
but I can't handle with the second one.
May I use reduce here?
You can use a closure and an IIFE to store the sum
Object.entries(obj).filter((() => {
let sum = 0;
return ([k, v]) => { sum += v; return v !== 0 && sum < 10; };
})());
Examples:
function convert(obj) {
return Object.entries(obj).filter((() => {
let sum = 0;
return ([k, v]) => { sum += v; return v !== 0 && sum < 10; };
})());
}
const obj = { a: 5, b: 3, c: 0, d: 9 };
const arr = convert(obj);
console.log(arr);
const obj2 = { a: 0, b: 0, c: 8, d: 0, e: 1, f: 5 };
const arr2 = convert(obj2);
console.log(arr2);
const obj3 = { a: 12 };
const arr3 = convert(obj3);
console.log(arr3);
#jabaa's answer is great and you should accept it.
Just to confirm your intuition, you could have used reduce, but it would get rather complicated:
const obj = {
a: 5,
b: 3,
c: 0,
d: 9
}
const result = Object.entries(obj).reduce(
(o, newPair) => {
o.sum += newPair[1];
newPair[1] !== 0 && o.sum < 10 && o.pairs.push(newPair);
return o;
},
{
sum: 0,
pairs: []
}
).pairs;
console.log(result)
I am trying to compare two objects but only with three keys instead of all keys. It looks like this:
Object.keys(StateA)
.filter((k) => [k == 'name', 'x', 'y'])
.every((k) => StateA[k] == StateB[k])
)
I am getting false results; what I am doing wrong?
There's no need to filter keys if you already have/know the ones to compare beforehand; use every just as you are:
const A = { a: 0, b: 1, c: 2, x: 3, y: 4, z: 5 };
const B = { a: 0, b: 2, c: 3, x: 3, y: 4, z: 6 };
const match = ['a', 'x', 'y'].every(key => A[key] === B[key]);
console.log(match);
Keep in mind a simple check like this may give you false positives - it depends on what you want. One case would be a key missing in one object but present in the other set to undefined. If that's the case, you may want to also check for the presence of the key:
const A = { a: 0, b: 1, c: undefined };
const B = { a: 0, b: 1 };
const keys = ['a', 'b', 'c'];
const match = keys.every(key => A[key] === B[key]);
console.log(match); // true
const stricterMatch = keys.every(key => (
key in A && key in B && A[key] === B[key]
));
console.log(stricterMatch); // false
export function hasSameProps (source: Record<string,unknown>, target: Record<string,unknown>) {
Object.keys(source).every(key => target.hasOwnProperty(key));
or
for (const key in ObjA) {
const current = ObjB[key];
if (!current) {
// does not exists
}
}
So I have this data:
fields = ['a', 'b', 'c']
data = [{r: 1, a: 2, b: 3, c: 4, h: 5}, {r: 4, a: 9, b: 1, c: 4, h: 5} ... ]
and I want to be able (preferred with lodash) to be able to get to this:
newData = [{r:1, h:5, values: [{name: 'a', value: 2},{name: 'b', value: 3}, {name: 'c', value: 4}], .....]
Meaning only the fields from the 'fields' object be taken out of each object in array (they always exist) and put into 'values' property that has an array of them in the format displayed here.
Would love to hear suggestions of the cleanest way to achieve this!
I did this :
function something(data, fields) {
const formattedData = _.map(data, (currData) => {
const otherFields = _.omit(currData, fields)
return {
...otherFields,
values: _.flow(
currData => _.pick(currData, fields),
pickedFields => _.toPairs(pickedFields),
pairs => _.map(pairs, pair => {
return { name: pair[0], value: pair[1] }
})
)(currData)
}
})
return formattedData
}
which works, but I'm wondering if it isn't a bit complicated.
The _.flow() method creates a function, which you can extract and name. In addition, the 1st function in the flow, accepts more than 1 parameter, so you don't need to pass it explicitly. Since _.toPairs() is unary, you don't need to wrap it in an arrow function.
The object creation is a bit annoying. I've used _.zipObject(), but it's still cumbersome.
Now you can use the function create by _.flow() in your main function, and it's pretty readable:
const { flow, pick, toPairs, map, partial, zipObject, omit } = _
const propsToObjs = flow(
pick,
toPairs,
pairs => map(pairs, partial(zipObject, ['name', 'value'])),
)
const fn = (data, fields) =>
map(data, currData => ({
...omit(currData, fields),
values: propsToObjs(currData, fields)
}))
const fields = ['a', 'b', 'c']
const data = [{r: 1, a: 2, b: 3, c: 4, h: 5}, {r: 4, a: 9, b: 1, c: 4, h: 5}]
const result = fn(data, fields)
console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.js"></script>
Using lodash/fp, we can make the flow function even nicer, since lodash/fp functions are auto-curried and iteratee-first data-last (not the reversed order of parameters):
const { flow, pick, toPairs, map, partial, zipObject, omit } = _
const propsToObjs = flow(
pick,
toPairs,
map(zipObject(['name', 'value']))
)
const fn = fields => map(currData => ({
...omit(fields, currData),
values: propsToObjs(fields, currData)
}))
const fields = ['a', 'b', 'c']
const data = [{r: 1, a: 2, b: 3, c: 4, h: 5}, {r: 4, a: 9, b: 1, c: 4, h: 5}]
const result = fn(fields)(data)
console.log(result)
<script src='https://cdn.jsdelivr.net/g/lodash#4(lodash.min.js+lodash.fp.min.js)'></script>
You could map through the objects in data and then check if the key is in the fields array:
fields = ["a", "b", "c"];
data = [
{ r: 1, a: 2, b: 3, c: 4, h: 5 },
{ r: 4, a: 9, b: 1, c: 4, h: 5 },
];
let newData = data.map((o) => {
let newObject = {};
newObject.values = [];
for (let k in o) {
if (fields.includes(k)) {
newObject.values.push({
name: k,
value: o[k]
});
} else {
newObject[k] = o[k];
}
}
return newObject;
});
console.log(newData);
You could destructure the object, pick the wanted properties and return the rest of the object with wanted values.
const
fields = ['a', 'b', 'c'],
data = [{ r: 1, a: 2, b: 3, c: 4, h: 5 }, { r: 4, a: 9, b: 1, c: 4, h: 5 }],
result = data.map(o => {
const values = fields.map(name => {
let value;
({ [name]: value, ...o } = o);
return { name, value };
});
return { ...o, values };
});
console.log(result);
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