Ternary operator return nothing - javascript

is there a way to return nothing for ternary operator I mean
const a = [ 0 ? { name : "example" } : null ]
when i print a = [null]
or:
const a = [ 0 && {name:"example"}]
a will be [false]
i expected that a = [] for case 1

You could spread an (empty) array.
console.log([...(0 ? [{ name : "example" }] : [])]);
console.log([...(1 ? [{ name : "example" }] : [])]);

No. It isn't possible. You are going to get a value back.
If you conditionally want a value, then either make the decision outside the array or filter the null values out afterwards.
e.g.
const a = 0 ? [ { name: "example" } ] : [];
or
const a = [ 0 ? { name : "example" } : null ].filter(Boolean);

null is a perfectly valid array value in Javascript, as is undefined.
You can simply construct the array on demand...
const a = 0 ? [{ name : "example" }] : [];
or if this is part of a larger array construction, use splats...
const a = [
'a',
...(0 ? [{name : "example"}] : []),
'b'
];
console.log(a); //-> ['a', 'b']

Related

How to conditionally add or remove element inside an array

I don't want second element null in else condition .. i just don't want second element.
How to solve this issue?
var template = "";
var myArray = [
{ element : "header" },
template === 'foo' ? { element : "sidebar" } : null,
{ element : "footer" }
]
console.log(myArray)
There something called conditional spread operator and it's perfect for your issue
When condition is false you spread empty array so literally nothing is added to array you declare
const template1=""
const myArray1 = [
{ element : "header" },
...( template1 === 'foo' ? [{ element : "sidebar" }] : [] ),
{ element : "footer" }
]
console.log(myArray1)
const template2="foo"
const myArray2 = [
{ element : "header" },
...( template2 === 'foo' ? [{ element : "sidebar" }] : [] ),
{ element : "footer" }
]
console.log(myArray2)
I like the spread operator in the other example
For compatibility, just use an if:
var template1 = "foo";
var myArray1 = [
{ element : "header" },
{ element : "footer" }
]
if (template1 === 'foo') myArray1.splice(1,0,{ element : "sidebar" })
console.log(myArray1)
var template2 = "";
var myArray2 = [
{ element : "header" },
{ element : "footer" }
]
if (template2 === 'foo') myArray2.splice(1,0,{ element : "sidebar" })
console.log(myArray2)
const template = '';
const myArray = [
{ element : "header" },
{ element : "footer" },
...(template === 'foo' ? [{ element : "sidebar" }] : [])
]
console.log(myArray)
You can spread a ternary condition inside the array, with an empty array as a falsy case.

Map through an inner array of an Object

I have this object:
let arr = [{
id : 1,
usr : 'pimba',
xyz: null
},
{
id : 2,
usr : 'aloha',
xyz: {
xyz_id: 2
}
},
{
id : 3,
age : 'pruu',
xyz: null
}];
As you can notice, sometimes xyz is null and sometimes it's not.
I need to recognize whether it is null or not, so I can read it.
I was trying to use map() function but I can't set some sort of filter to only execute the annonymous function when it is NOT null.
I managed to do something like this:
let result = Object.values(arr).map(function(row){
if(row['xyz'] != null) {
console.log(row['xyz_id']);
}
});
what If I want a new array containing ONLY xyz_id ? Is there a shorter version ?
Second case:
There are more than 1 value inside xyz and it's NOT "named".
let arr = [{
id : 1,
usr : 'pimba',
xyz: null
},
{
id : 2,
usr : 'aloha',
xyz: {
xyz_id: {"value1Here", "Value2Here"}
}
},
{
id : 3,
age : 'pruu',
xyz: null
}];
It seems you want to map the array only for the elements that have not-null xyz property. One option is using both .filter and .map methods. Another option is using the .reduce method:
let result = arr.reduce(function(ret, row) {
// assuming `xyz` can be only `null` or an object
if ( row.xyz !== null ) {
ret.push(row.xyz.xyz_id);
}
return ret;
}, []);
You might want to look at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
const notNull = arr.filter(elm => elm.xyz !== null);
var a = {one: 1, two: null, three: 3, four: true}
var y = []
let scan = (obj) => {
Object.keys(obj).forEach(x => {
if (obj[x] === null) {
console.log('Its null')
} else {
// Extend here to datatypes
y.push(obj[x])
}
});
}
scan(a)
console.log(y)

Ramda (or other FP lib) usage for selecting maybe null keys

Let's say I have a data structure like:
let slots = {
7 : [ 'a', 'b', 'c' ],
8 : [ 'd', 'e', 'f' ]
}
let names = {
a : { name : 'Joe' },
b : { name : 'Doe' },
c : { name : 'Cecilia' },
d : { name : 'Hugh' }
}
... where slots[x][y] is correlated to names' keys.
Given that x and y are inputs that can rannge from 0 to 10, one would write, in order to get the names and account for the error cases:
let nameKey = (slots[x] || [])[y] //string or undefined
let name = (names[nameKey] || {}).name || ''
So here I've used things like || [] or || {} in order to avoid probable errors with some inputs and null keys. I've heard that by using FP kits I can also achieve that in a cleaner way. What functions of Ramda (or any other FP kit) should I use in order to achieve that?
Ramda has pathOr:
let slots = {
7 : [ 'a', 'b', 'c' ],
8 : [ 'd', 'e', 'f' ]
}
let names = {
a : { name : 'Joe' },
b : { name : 'Doe' },
c : { name : 'Cecilia' },
d : { name : 'Hugh' }
}
You'd do:
let nameKey = R.pathOr(undefined, [x, y], slots);
//it'd be probably better to normalize it to always a string instead of undefined (but that's what you wrote)
let name = R.pathOr('', [nameKey, 'name'], names);

Javascript multiple condition array filter

I need help putting together an array search that is based on multiple conditions. Furthermore, all the conditions are conditional, meaning I may or may not need to filter on those conditions. What I have:
Array of objects to filter:
var data = [{
"_id" : ObjectId("583f6e6d14c8042dd7c979e6"),
"transid" : 1,
"acct" : "acct1",
"transdate" : ISODate("2012-01-31T05:00:00.000Z"),
"category" : "category1",
"amount" : 103
},
{
"_id" : ObjectId("583f6e6d14c8042dd7c2132t6"),
"transid" : 2,
"acct" : "acct2",
"transdate" : ISODate("2012-01-31T05:00:00.000Z"),
"category" : "category2",
"amount" : 103
},
{
"_id" : ObjectId("583f6e6d14c8042dd7c2132t6"),
"transid" : 3,
"acct" : "acct2",
"transdate" : ISODate("2016-07-31T05:00:00.000Z"),
"category" : "category1",
"amount" : 103
},
{
"_id" : ObjectId("583f6e6d14c8042dd7c2132t6"),
"transid" : 4,
"acct" : "acct2",
"transdate" : ISODate("2012-01-31T05:00:00.000Z"),
"category" : "category2",
"amount" : 103
},
{
"_id" : ObjectId("583f6e6d14c8042dd7c2132t6"),
"transid" : 5,
"acct" : "acct2",
"transdate" : ISODate("2012-01-31T05:00:00.000Z"),
"category" : "category3",
"amount" : 103
},
{
"_id" : ObjectId("583f6e6d14c8042dd7c152g2"),
"transid" : 6,
"acct" : "acct3",
"transdate" : ISODate("2016-10-31T05:00:00.000Z"),
"category" : "category3",
"amount" : 103
}]
I am filtering the above array of objects based on another array of mixed elements. The elements represent the following search fields:
"searchstring": to search on all fields in the data array for any
matched text sequence
object with key values reprsenting account type and a true or false
for value indicating if it should be used to filter
startdate to filter transdate on
enddate to filter transdate
category name to filter category on
The array that has the search conditions looks like this (but if some of the fields are not necessary they will be set to undefined or just an empty string or array):
var filtercondition = {
"p",
{acct1:true,acct2:false,acct3:true...}
"2016-06-01",
"2016-11-30",
"category3"
}
What is the best way to accomplish this? What I've devised is a separate search for each element in the filter array, but this seems non optimal and very tedious. I'm open to a redesign of my setup...
// You wrote that it's an array, so changed the braces
var filtercondition = ["p",
{acct1:true,acct2:false,acct3:true...}
"2016-06-01",
"2016-11-30",
"category3"
];
var filtered = data.filter(o => {
if(filtercondition[0] && !o.category.includes(filtercondition[o])) { // checking just the category, but you can check if any of more fields contains the conditions
return false;
}
if(filtercondition[1]) {
for(var key in filtercondition[1]) {
if(filtercondition[1][key] === true && o.acct != key) {
return false;
}
}
}
if(filtercondition[2] && o.transdate < filtercondition[2]) {
return false;
}
if(filtercondition[3] && o.transdate > filtercondition[3]) {
return false;
}
if(filtercondition[4] && o.category !== filtercondition[4]) {
return false;
}
return true;
});
Two notes:
- changed the braces of filtercondition so that it is an array, however I would suggest to use an object instead.
- this {acct1:true,acct2:false,acct3:true...} sample doesn't make sense for me, since it suggests that the acct field should be acct1 and acct3 at the same time.
Create an array of functions, each function representing a condition.
Here's some sample code which demonstrates the approach...
var conditions = [];
// Dynamically build the list of conditions
if(startDateFilter) {
conditions.push(function(item) {
return item.transdate >= startDateFilter.startDate;
});
};
if(categoryFilter) {
conditions.push(function(item) {
return item.cateogry === categoryFilter.category;
});
};
// etc etc
Once you have an array of conditions, you can use Array.prototype.every to run each condition on an item.
var itemsMatchingCondition = data.filter(function(d) {
return conditions.every(function(c) {
return c(d);
});
});
Or, using the more compact arrow functions:
const itemsMatchingCondition = data.filter(d => conditions.every(c => c(d));
First, you'll want to use brackets for your array not curly braces:
var filtercondition = [
"p",
{acct1:true,acct2:false,acct3:true...},
"2016-06-01",
"2016-11-30",
"category3"
];
Then again, I don't think that an array is the best data type for that. Try an object like this:
var filtercondition = {
query: "p",
accounts: {acct1:true,acct2:false,acct3:true...},
date1: "2016-06-01",
date2: "2016-11-30",
category: "category3"
};
Then, try using Array.prototype.filter:
var filtered = data.filter(function(obj) {
for (var key in filtercondition) {
// if condition not met return false
}
return true;
});
I'd go with a bunch of small granular functions and compose them.
//only some utilities, from the top of my mind
var identity = v => v;
//string-related
var string = v => v == null? "": String(v);
var startsWith = needle => haystack => string(haystack).startsWith(needle);
var endsWith = needle => haystack => string(haystack).endsWith(needle);
var contains = needle => haystack => string(haystack).contains(needle);
//do sth with an object
var prop = key => obj => obj != null && prop in obj? obj[prop]: undefined;
var someProp = fn => obj => obj != null && Object.keys(obj).some(k => fn(k) );
var someValue = fn => obj => obj != null && Object.keys(obj).some(k => fn(obj[k]) );
//logic
var eq = b => a => a === b;
var not = fn => function(){ return !fn.apply(this, arguments) };
var and = (...funcs) => funcs.reduce((a, b) => function(){
return a.apply(this, arguments) && b.apply(this, arguments);
});
var or = (...funcs) => funcs.reduce((a, b) => function(){
return a.apply(this, arguments) || b.apply(this, arguments);
});
//composition
var compose = (...funcs) => funcs.reduce((a, b) => v => return a(b(v)));
var chain = (...funcs) => funcs.reduceRight((a, b) => v => return a(b(v)));
//and whatever else you want/need
//but stay granular, don't put too much logic into a single function
and an example composition:
var filterFn = and(
//some value contains "p"
someValue(contains("p")),
//and
chain(
//property "foo"
prop("foo"),
or(
//either contains "asdf"
contains("asdf"),
//or startsWith "123"
startsWith("123")
)
),
)
since I don't know how you build your filterconditions, I cannot tell you exactly how to parse them into such a composition, but you could compose them like this:
//start with something basic, so we don't ever have to check wether filterFn is null
var filterFn = identity;
//and extend/compose it depending on some conditions
if(/*hasQuery*/){
filterFn = and(
// previous filterFn(obj) && some value on obj contains `query`
filterFn,
someValue(contains(query)))
)
}
if(/*condition*/){
//extend filterFn
filterFn = or(
// (obj.foo === null) || previous filterFn(obj)
chain(prop("foo"), eq(null)),
filterFn
);
}
and so on
First, some points:
Your data object is invalid if you're going to use it in the browser. Probably the data comes from MongoDB, right? Your backend (data source) should have a method to encode it properly and remove ObjectID and ISODate references.
Your filtercondition is not a valid JavaScript object/JSON. Check my example.
So, you can filter your data array with Array#filter method.
Something like that:
let data = [{
"_id" : "583f6e6d14c8042dd7c979e6",
"transid" : 1,
"acct" : "acct1",
"transdate" : "2012-01-31T05:00:00.000Z",
"category" : "category1",
"amount" : 103
},
{
"_id" : "583f6e6d14c8042dd7c2132t6",
"transid" : 2,
"acct" : "acct2",
"transdate" : "2012-01-31T05:00:00.000Z",
"category" : "category2",
"amount" : 103
},
{
"_id" : "583f6e6d14c8042dd7c2132t6",
"transid" : 5,
"acct" : "acct2",
"transdate" : "2012-01-31T05:00:00.000Z",
"category" : "category3",
"amount" : 103
}];
let filterToApply = {
acct: {
acct1: true,
acct2: false,
acct3: true
},
initialDate: "2016-06-01",
finalDate: "2016-11-30",
category: "category3"
}
let filterData = (array, filter) => {
return array.filter( (item) => {
/* here, you iterate each item and compare with your filter,
if the item pass, you must return true. Otherwise, false */
/* e.g.: category check (if present only) */
if (filter.category && filter.category !== item.category)
return false;
}
/* add other criterias check... */
return true;
});
}
let dataFiltered = filterData(data, filterToApply);
console.log(dataFiltered);
If you want to filter an array with multiple conditions and the conditions may be optional, then use the following method.
const data = [
{ name: 'John', age: 25, city: 'New York' },
{ name: 'John', age: 25, city: 'New' },
{ name: 'Jane', age: 32, city: 'Los Angeles' },
{ name: 'Bob', age: 45, city: 'New York' },
{ name: 'Alice', age: 38, city: 'Los Angeles' }
];
const filteredData = (n, c, a) => data.filter(item => {
if (n || c || a) {
return (n ? item.name === n : true) && (c ? item.city === c : true) && (a ? item.age === a : true); // keep adding conditons as much as u want
}
});
console.log(filteredData('John', null, 25));
console.log(filteredData(null, 'Los Angeles', 38));
console.log(filteredData(null, 'Los Angeles', null));
You can chain as many as conditions

Remove duplicate object from array javascript [duplicate]

I have this kind of array:
var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
I'd like to filter it to have:
var bar = [ { "a" : "1" }, { "b" : "2" }];
I tried using _.uniq, but I guess because { "a" : "1" } is not equal to itself, it doesn't work. Is there any way to provide underscore uniq with an overriden equals function?
.uniq/.unique accepts a callback
var list = [{a:1,b:5},{a:1,c:5},{a:2},{a:3},{a:4},{a:3},{a:2}];
var uniqueList = _.uniq(list, function(item, key, a) {
return item.a;
});
// uniqueList = [Object {a=1, b=5}, Object {a=2}, Object {a=3}, Object {a=4}]
Notes:
Callback return value used for comparison
First comparison object with unique return value used as unique
underscorejs.org demonstrates no callback usage
lodash.com shows usage
Another example :
using the callback to extract car makes, colors from a list
If you're looking to remove duplicates based on an id you could do something like this:
var res = [
{id: 1, content: 'heeey'},
{id: 2, content: 'woah'},
{id: 1, content:'foo'},
{id: 1, content: 'heeey'},
];
var uniques = _.map(_.groupBy(res,function(doc){
return doc.id;
}),function(grouped){
return grouped[0];
});
//uniques
//[{id: 1, content: 'heeey'},{id: 2, content: 'woah'}]
Implementation of Shiplu's answer.
var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
var x = _.uniq( _.collect( foo, function( x ){
return JSON.stringify( x );
}));
console.log( x ); // returns [ { "a" : "1" }, { "b" : "2" } ]
When I have an attribute id, this is my preffered way in underscore:
var x = [{i:2}, {i:2, x:42}, {i:4}, {i:3}];
_.chain(x).indexBy("i").values().value();
// > [{i:2, x:42}, {i:4}, {i:3}]
Using underscore unique lib following is working for me, I m making list unique on the based of _id then returning String value of _id:
var uniqueEntities = _.uniq(entities, function (item, key, a) {
return item._id.toString();
});
Here is a simple solution, which uses a deep object comparison to check for duplicates (without resorting to converting to JSON, which is inefficient and hacky)
var newArr = _.filter(oldArr, function (element, index) {
// tests if the element has a duplicate in the rest of the array
for(index += 1; index < oldArr.length; index += 1) {
if (_.isEqual(element, oldArr[index])) {
return false;
}
}
return true;
});
It filters out all elements if they have a duplicate later in the array - such that the last duplicate element is kept.
The testing for a duplicate uses _.isEqual which performs an optimised deep comparison between the two objects see the underscore isEqual documentation for more info.
edit: updated to use _.filter which is a cleaner approach
The lodash 4.6.1 docs have this as an example for object key equality:
_.uniqWith(objects, _.isEqual);
https://lodash.com/docs#uniqWith
Try iterator function
For example you can return first element
x = [['a',1],['b',2],['a',1]]
_.uniq(x,false,function(i){
return i[0] //'a','b'
})
=> [['a',1],['b',2]]
here's my solution (coffeescript) :
_.mixin
deepUniq: (coll) ->
result = []
remove_first_el_duplicates = (coll2) ->
rest = _.rest(coll2)
first = _.first(coll2)
result.push first
equalsFirst = (el) -> _.isEqual(el,first)
newColl = _.reject rest, equalsFirst
unless _.isEmpty newColl
remove_first_el_duplicates newColl
remove_first_el_duplicates(coll)
result
example:
_.deepUniq([ {a:1,b:12}, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ],[ 2, 1, 2, 1 ], {a:1,b:12} ])
//=> [ { a: 1, b: 12 }, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ] ]
with underscore i had to use String() in the iteratee function
function isUniq(item) {
return String(item.user);
}
var myUniqArray = _.uniq(myArray, isUniq);
I wanted to solve this simple solution in a straightforward way of writing, with a little bit of a pain of computational expenses... but isn't it a trivial solution with a minimum variable definition, is it?
function uniq(ArrayObjects){
var out = []
ArrayObjects.map(obj => {
if(_.every(out, outobj => !_.isEqual(obj, outobj))) out.push(obj)
})
return out
}
var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
var bar = _.map(_.groupBy(foo, function (f) {
return JSON.stringify(f);
}), function (gr) {
return gr[0];
}
);
Lets break this down. First lets group the array items by their stringified value
var grouped = _.groupBy(foo, function (f) {
return JSON.stringify(f);
});
grouped looks like:
{
'{ "a" : "1" }' = [ { "a" : "1" } { "a" : "1" } ],
'{ "b" : "2" }' = [ { "b" : "2" } ]
}
Then lets grab the first element from each group
var bar = _.map(grouped, function(gr)
return gr[0];
});
bar looks like:
[ { "a" : "1" }, { "b" : "2" } ]
Put it all together:
var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
var bar = _.map(_.groupBy(foo, function (f) {
return JSON.stringify(f);
}), function (gr) {
return gr[0];
}
);
You can do it in a shorthand as:
_.uniq(foo, 'a')

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