I have a javascript method, where I'm trying to group my data by 'date', which works fine.
But when I look at the length of my object it shows, 'zero'.
Is there a better way to do this? and keep the length of the new variable?
groupByDate(snapshot) {
let list = []
this.orders.reduce(function (a, c) {
if(!list[c.date]) {
list[c.date] = [];
}
list[c.date].push(c);
});
this.ordersByDate = list
console.log(list)
}
You are pushing properties into an array. You are not setting the indexes of the array. So you should be using an object and not an array. Your use of reduce is also not correct. You are treating it like a forEach loop.
So use an object and use reduce the way it is supposed to be
let list = this.orders.reduce(function (o, c) {
o[c.date] = o[c.date] || []
o[c.date].push(c)
return o
}, {})
console.log(Object.keys(list).length)
I would use a dictionary (key, values) for that:
list {
date1: [obj1-1, obj1-2, ...],
date2: [obj2-1, obj2-2, ...],
...
}
list = {};
this.orders.forEach(order => {
if (!list.hasOwnProperty(order.date)) {
// If it is the first time we meet this date, create an array with th first element
list[order.date] = [order];
} else {
// We have already meet the date, thus the key exists and so do the array. Add element to array
list[order.date].push(order);
}
});
It seems you have an array and its indexes are the dates. I assume the dates are big numbers (date from 1970 in milliseconds, something like that), which may lead to having a very very big array 99,9% empty. That is why according to me you should use an object and not an array.
Or maybe those are not dates but id's of dates ?
Related
I have two arrays created from a reduce method that searches two existing arrays for dates. It then turns those dates into unique object keys.
The first group is a list of names the second is a set of series of instructions.
The goal is to combine the two arrays that get formed by finding like object keys and adding the matching list object and insert it into the set of instructions with the object key list.
For one it makes an array that looks like :
const listObj = [
{11/20/2020: [{name:'Joe', date:11/20/2020}]},
{11/26/2020 : [{name:'John', date:11/26/2020}]}
]
And this:
const scheduleObj = [
{11/20/2020: {type:'Federal', date:11/20/2020}},
{11/26/2020 : {type:'State', date:11/26/2020}}
]
The final product that i need would look something like:
const scheduleObj = [
{11/26/2020 : {
type: 'State',
list: [{name:'John', date:11/26/2020}]
},
...
]
Where the list is an added key and the array is the array that is associated with the object key
I have used a messy what looks like lodash method to get this to work, but I figure there has to be some sort of mapping I can do.
Any Help Would Be Appreciated
This can be little messy and not failure proof depending on what you have in your listObj or scheduleObj. E.g. repeated date in scheduleObj can lead to a problem using this method, you may have to use another key if the dates are no unique in both lists.
scheduleObj.map((s) => {
// get the first key of the object as the date you're going to group with
const date = Object.keys(s)[0];
// filter the object that matches the date
const listObjFilter = listObj.filter((o) => Object.keys(o)[0] === date);
// get the list for the given date (or empty array if nothing found)
const listForDate = listObjFilter.length ? listObjFilter[0][date] : [];
// build the result object
return {
[date]: {
type: s[date]['type'],
list: listForDate
}
};
})
Note that I'm always considering you have only one key in the objects inside the lists in listObj or scheduleObj.
Title is pretty much self explanatory...
I want to be able to find duplicated values from JavaScript array.
The array keys can be duplicated so I need to validate only the array values.
Here is an example :
var arr=[
Ibanez: 'JoeSatriani',
Ibanez: 'SteveVai',
Fender: 'YngwieMalmsteen',
Fender: 'EricJohnson',
Gibson: 'EricJohnson',
Takamine: 'SteveVai'
];
In that example:
the key is the guitar brand
the value is the guitar player name.
So:
If there is duplicated keys (like: Ibanez or Fender) as on that current example that is OK :-)
But
If there is duplicated values (like: EricJohnson or SteveVai) I'm expecting to get (return) that error:
EricJohnson,SteveVai
You can't have associative arrays in Javascript. You can create an array of objects, like:
var arr=[
{Ibanez: 'JoeSatriani'},
{Ibanez: 'SteveVai'},
{Fender: 'YngwieMalmsteen'},
{Fender: 'EricJohnson'},
{Gibson: 'EricJohnson'},
{Takamine: 'SteveVai'}
];
Then you'll need a for...in loop to go over every object in the array, create a new array of values and check that for duplicates, which is also not very straightforward - basically you'll want to sort the array and make sure no value is the same as the one after it.
var arrayOfValues = [];
arr.forEach(function(obj){
for(var prop in obj)
arrayOfValues.push(obj[prop]);
});
arrayOfValues.sort(); // by default it will sort them alphabetically
arrayOfValues.forEach(function(element,index,array){
if(array[index+1] && element==array[index+1])
alert("Duplicate value found!");
});
First of all, object keys can not be repeated.
This means that:
({
"Fender": "Jim",
"Fender": "Bob"
})["Fender"]
Would simply return: "Bob".
However, I did make a code that could allow you to find duplicates in values, but as I said, the key will have to be unique:
var arr = {
Ibanez: 'EricJohnson',
Fender: 'YngwieMalmsteen',
Gibson: 'EricJohnson',
Takamine: 'SteveVai',
"Takamine2": 'SteveVai'
};
function contains(a, obj) {
for (var i = 0; i < a.length; i++) {
if (a[i] === obj) {
return true;
}
}
return false;
}
var track = [];
var exists = [];
for (var val in arr) {
if (contains(track, arr[val])) {
exists.push(arr[val]);
} else {
track.push(arr[val])
}
}
alert(exists)
You can see it working here: http://jsfiddle.net/dr09sga6/2/
As others have commented, the example array you provided isn't a valid JavaScript array. You could, however, keep a list for each guitar type:
var mapping = {
Ibanez: ['JoeSatriani','SteveVai'],
Fender: ['YngwieMalmsteen','EricJohnson']
Gibson: ['EricJohnson'],
Takamine: ['SteveVai']
];
Or a list of each guitar/musician pair:
var pairs = [
['Ibanez','JoeSatriani'],
['Ibanez','SteveVai'],
['Fender','YngwieMalmsteen'],
['Fender','EricJohnson'],
['Gibson','EricJohnson'],
['Takamine','SteveVai']
];
Your solution is going to depend on which pattern you go with. However, in the second case it can be done in one chained functional call:
pairs.map(function(e) {return e[1]}) // Discard the brand names
.sort() // Sort by artist
.reduce(function(p,c,i,a){
if (i>0 && a[i]==a[i-1] && !p.some(function(v) {return v == c;})) p.push(c);
return p;
},[]); //Return the artist names that are duplicated
http://jsfiddle.net/mkurqmqd/1/
To break that reduce call down a bit, here's the callback again:
function(p,c,i,a){
if (i>0
&& a[i]==a[i-1]
&& !p.some(function(v) {
return v == c;
}))
p.push(c);
return p;
}
reduce is going to call our callback for each element in the array, and it's going to pass the returned value for each call into the next call as the first parameter (p). It's useful for accumulating a list as you move across an array.
Because we're looking back at the previous item, we need to make sure we don't go out of bounds on item 0.
Then we're checking to see if this item matches the previous one in the (sorted) list.
Then we're checking (with Array.prototype.some()) whether the value we've found is ALREADY in our list of duplicates...to avoid having duplicate duplicates!
If all of those checks pass, we add the name to our list of duplicate values.
Suppose I have an object with this structure:
{
"friends_count": {
"1420800660": 49391,
"1421149814": 49344,
"1421149955": 49344
}
}
In the object, the first number (the key) is a timestamp. The second number is the value. I want to get the most recent item of that object. So, I need to get the key that is closest in time. How do I have to do it?
So, I need to get the key that is closest in time
Sure. Just call Object.keys on obj.friends_count and then sort
var key = Object.keys(obj.friends_count).sort()[0];
Object.keys returns an array of keys of the provided object and Array.sort will sort it in ascending order and [0] will take the first element of the sorted array.
Just Array.sort will work fine here since they are of the same length and everything should be fine. If you want to be more clear, then it would be arr.sort(function(a, b){ return a - b })[0]
If you are wanting to get the latest from the key timestamp then just convert it to a date:
var something = {
"friends_count": {
"1420800660": 49391,
"1421149814": 49344,
"1421149955": 49344
}
},
dateCheck,
newest;
for(var key in something.friends_count){
if(!dateCheck || new Date(key*1000) > dateCheck){
dateCheck = new Date(key*1000);
newest = something.friends_count[key];
}
}
console.log(newest);
http://jsfiddle.net/w4dsk4m3/
Suppose an array named myArray containing several values but no duplicates.
Suppose I want to push a value into it only if it won't lead to duplicates presence.
How I determinate duplicates => by comparing value's id.
I thought about Lodash#uniq to do the trick:
myArray.push(aNewValue);
myArray = _.uniq(myArray,function(item){
return item.id;
});
However, I don't like the reassignment to the array and especially the fact that I have to push before checking...
Is there a more "functional" way to achieve it while being very short?
I don't want to iterate through the array explicitly in order to apply the check.
That's why I attempted to use Lodash.
You can check the presence of an item before adding it :
if(myArray.indexOf(aNewValue) == -1) {
myArray.push(aNewValue);
}
The most efficient way to do this is generally to use an object for uniqueness, because an object can have at most one key of a certain value. However, this is restricted to strings and things that stringify, since only strings can be object keys.
There are two approaches here. If you are using your array often, then you should keep parallel structures - an object for uniqueness check, an array for arrayness of it.
If you don't need your array often, i.e. you want to push a bunch of things and then have an array be unique, you can just use the object, and transform it into an array when you need it (which is somewhat expensive, so you only want to do it once, but still cheaper than manipulating two different structures all the time).
The first approach is illustrated here:
function Set() {
this.presence = {};
this.array = [];
};
Set.prototype.push = function(key, value) {
if (this.presence[key]) return;
this.presence[key] = true;
this.array.push(value);
};
var a = new Set();
a.push(3, { id: 3, value: "SOMETHING" });
a.push(7, { id: 7, value: "SOMETHING ELSE" });
a.push(3, { id: 3, value: "SOMETHING" });
console.log(a.array); // => only 2 elements
The second, here:
function Set() {
this.store = {};
};
Set.prototype.push = function(key, value) {
this.store[key] = value;
};
Set.prototype.array = function() {
var that = this;
return Object.keys(this.store).map(function(key) { return that.store[key]; })
};
...
console.log(a.array()); // note the newly added parentheses :)
Both of these are still cheaper than looking for presence inside the array using indexOf, even more so when you do your own iterating, except very much maybe in case the array is very short.
You could use Array.prototype.some() to find out if the value is already part of the array, e.g.:
if( myArray.some(function (elem) { return elem.id == newValue.id }) )
myArray.push(newValue);
You can't really get away with not looping through the array, though.
The example code below uses a mix of razor and Javascript. The RenderChart function takes in dates. The dates var returns an array of dates. I'm wondering how I can check all the date arrays combined to see if any of them contain any items or in this case date strings.
foreach (MeasurementTypeGroup group in Model.MeasurementTypeGroups){
var dates = #(Html.Raw(dates)); // dates returns []
RenderChart( dates);
console.log(dates); //console would display something like " [] [] [] or [] [3/2/12] []
}
Initially I was using an if condition to check the length
if(dates.length === undefined || dates.length === 0) {
//do something
}
this partially works, but it does this on every iteration in the foreach loop rather than on a total of all the date arrays. I'm guessing I need to return another variable and then push the contents of one into the other but I'm having an issue figure out how to do this. Thanks for any help!
you can use concat to combine all the arrays into a single one.
http://www.w3schools.com/jsref/jsref_concat_array.asp
var allDates = []
foreach (MeasurementTypeGroup group in Model.MeasurementTypeGroups){
var dates = #(Html.Raw(dates)); // dates returns []
allDates.concat(dates);
}
RenderChart(allDates);