I'm trying to add an item in a specific index inside an array inside a map function and it's been behaving unexpectedly. Here's the code for it
const addItemToLevelTwoArray= (uniqueID, arrayID )=> {
const reportObject = {
id:arrayID,
title:'',
}
data.map(section=>{
section.content.map((report, reportIndex)=>{
if(report.id===uniqueID){
section.content.splice(reportIndex, 0, reportObject);
}
return report;
})
return section;
})
}
Here's a working pen - https://codepen.io/raufabr/pen/vYZYgOV?editors=0011
Expected behaviour is that it would insert an object in the specific index, right above the object where the ID matches.
However, it's acting weirdly and sometimes I'm getting 2 items being added instead of one.
Any tip on what I'm doing would be massively appreciated! I know I'm close but I've been stuck on this for a while now and can't figure out what I'm doing wrong!
Preface: You're using map incorrectly. If you're not using the array that map builds and returns, there's no reason to use it; just use a loop or forEach. More in my post here. And one reason to use an old-fashioned for loop is that you're in control of iteration, which matters because...
However, it's acting weirdly and sometimes I'm getting 2 items being added instead of one.
That's because you're inserting into the array being looped by the map, so on the next pass, it picks up the entry you're adding.
If you do a simple loop, you can easily avoid that by incrementing the index when you insert, or by looping backward; here's the looping backward approach:
const addItemToLevelTwoArray = (uniqueID, arrayID) => {
const reportObject = {
id: arrayID,
title: "",
};
for (const section of data) {
for (let reportIndex = section.content.length - 1; reportIndex >= 0; --reportIndex) {
const report = section.content[reportIndex];
if (report.id === uniqueID) {
section.content.splice(reportIndex, 0, reportObject);
}
}
}
};
Because we're looping backward, we won't pick up the entry we just added on the next pass.
Since the outer loop doesn't have that problem, I used the more convenient for-of.
Since you asked about map, if you do use the array map returns, you can do this by returning an array with the two entries, and then calling flat on the array map builds. (This only works if the array doesn't already contain arrays, because they'll get flattened to.) This is common enough that it's combined in one function: flatMap. It's not what I'd do (I'd do a loop), but it's certainly feasible. Sticking with forEach and flatMap rather than using for-of and for:
const addItemToLevelTwoArray = (uniqueID, arrayID) => {
const reportObject = {
id: arrayID,
title: "",
}
data.forEach(section => {
section.content = section.content.flatMap(report => {
if (report.id === uniqueID) {
// Return the new one and the old one
return [reportObject, report];
}
// Return just the old one
return report;
});
});
};
That assumes it's okay to modify the section object. If it isn't, Alberto Sinigaglia's answer shows creating a new replacement object instead, which is handy in some sitautions.
You can just use flatMap:
const data = [
{
content: [
{
id: 1,
title: "a"
},{
id: 3,
title: "c"
},
]
}
]
const addItemToLevelTwoArray= (uniqueID, arrayID )=> {
const reportObject = {
id:arrayID,
title:'',
}
return data.map(section=> {
return {
...section,
content: section.content.flatMap( report =>
report.id === uniqueID
? [reportObject, report]
: report
)
}
}
)
}
console.log(addItemToLevelTwoArray(3, 2))
The following will extend the inner array .contentwithout modifying the original array data:
const data = [ {id: 0,title:'main',content:[{id:1,title:'Hello'},
{id:2,title:"World"}] } ];
const addItemToLevelTwoArray= (uniqueID, arrayID )=> {
const reportObject = {
id:arrayID,
title:'something new!',
}
return data.map(d=>(
{...d, content:d.content.reduce((acc, rep)=>{
if(rep.id===uniqueID) acc.push(reportObject);
acc.push(rep)
return acc;
},[]) // end of .reduce()
})); // end of .map()
}
const res=addItemToLevelTwoArray(1,123);
console.log(res);
Related
I have an object of newsfeed items like below.
[{'story_id':130,'pinned':0,....},{'story_id':131,'pinned':1,....},{'story_id':132,'pinned':0,....},{'story_id':133,'pinned':0,....}]
I need to primarily order the news stories by their story_id DESC. But if a story has the property 'pinned'=1 it needs to be first.
filtered_news_feed: function() {
var list= _.orderBy(this.feed_items, ['story_id'],'desc');
return list;
},
The above works, but how do I do pinned items first, then the rest? For some reason the below completely ignores the story_id
var list= _.orderBy(this.feed_items, ['pinned','story_id'],'desc');
Using Array#sort:
const arr = [ {'story_id':130,'pinned':0}, {'story_id':131,'pinned':1}, {'story_id':132,'pinned':0}, {'story_id':133,'pinned':0} ];
const sorted = arr.sort(
({ story_id: storyIdA, pinned: pinnedA }, { story_id: storyIdB, pinned: pinnedB }) =>
pinnedB - pinnedA || storyIdB - storyIdA
);
console.log(sorted);
You can achieve this results in many ways, one of them is:
filtered_news_feed: function() {
const pinnedItems = this.feed_items.filter(item => item.pinned === 1);
const normalItems = this.feed_items.filter(item => item.pinned === 0);
return [
...pinnedItems,
_.orderBy(normalItems, ['story_id'], 'desc')
];
}
First, separate pinned items from normal items. Then return merged array with pinned items at the beginning.
Note: I used modern features of ES here. You should compile it via babel or other tool.
I'm attempting to add an object at a specific point in my 'data' array which is this components state. The following isn't working, the array simply gets emptied.
addNewBulletAfterActive = () => {
const array = this.state.data;
const newBulletPoint = {
id: this.state.data.length += 1,
title: 'Click to add'
};
const newData = array.splice(this.state.activeBulletPointId, 0, newBulletPoint);
this.setState({
data: newData
});
}
The idea is that if I have a list of 10 bullet points, the user can click on the 4th bullet point and press enter to add a new bullet point directly after. I've not had any issues adding items to the end of the array but it looks like .splice is causing issues.
I believe this should do what you're after.
function addAfter(array, index, newItem) {
return [
...array.slice(0, index),
newItem,
...array.slice(index)
];
}
This function returns a new array with a new item inserted in the middle. It doesn't mutate your original array and so will play nicely with component's state and Redux.
You can then assign the output from this function to your state.
splice returns spliced items (which is empty since you splice 0 items) and mutates original array.
const newData = array.slice(0); // copy
newData.splice(this.state.activeBulletPointId, 0, newBulletPoint);
this.setState({
data: newData
});
I think this could be an easier and faster method to do this
/*Just plain JS*/
function AddAfter(array, newObject){
array.unshift(newObject);
}
/*In react If updating state*/
var _prev = this.state.your_array; //getting the current value for the state object
var newInfo = {id: 1, more: 'This is a new object'};
_prev.unshift(newInfo);
I am building a simple todo app, and I'm trying to get the assigned users for each task. But let's say that in my database, for some reason, the tasks id starts at 80, instead of starting at 1, and I have 5 tasks in total.
I wrote the following code to get the relationship between user and task, so I would expect that at the end it should return an array containing 5 keys, each key containing an array with the assigned users id to the specific task.
Problem is that I get an array with 85 keys in total, and the first 80 keys are undefined.
I've tried using .map() instead of .forEach() but I get the same result.
let assignedUsers = new Array();
this.taskLists.forEach(taskList => {
taskList.tasks.forEach(task => {
let taskId = task.id;
assignedUsers[taskId] = [];
task.users.forEach(user => {
if(taskId == user.pivot.task_id) {
assignedUsers[taskId].push(user.pivot.user_id);
}
});
});
});
return assignedUsers;
I assume the issue is at this line, but I don't understand why...
assignedUsers[taskId] = [];
I managed to filter and remove the empty keys from the array using the line below:
assignedUsers = assignedUsers.filter(e => e);
Still, I want to understand why this is happening and if there's any way I could avoid it from happening.
Looking forward to your comments!
If your taskId is not a Number or autoconvertable to a Number, you have to use a Object. assignedUsers = {};
This should work as you want it to. It also uses more of JS features for the sake of readability.
return this.taskLists.reduce((acc, taskList) => {
taskList.tasks.forEach(task => {
const taskId = task.id;
acc[taskId] = task.users.filter(user => taskId == user.pivot.task_id);
});
return acc;
}, []);
But you would probably want to use an object as the array would have "holes" between 0 and all unused indexes.
Your keys are task.id, so if there are undefined keys they must be from an undefined task id. Just skip if task id is falsey. If you expect the task id to possibly be 0, you can make a more specific check for typeof taskId === undefined
this.taskLists.forEach(taskList => {
taskList.tasks.forEach(task => {
let taskId = task.id;
// Skip this task if it doesn't have a defined id
if(!taskId) return;
assignedUsers[taskId] = [];
task.users.forEach(user => {
if(taskId == user.pivot.task_id) {
assignedUsers[taskId].push(user.pivot.user_id);
}
});
});
});
I have this algorithme issue, I would like to check if an Object is already present in my Array before adding it.
I tried many different approaches (indexOf, filter...), and my last attempt is with an angular.foreach.
The problem is my $scope.newJoin remains always empty. I understood why, it's because the if is never read, because of the 0 size of my $scope.newJoin, but I don't know how to figure this out...
$scope.newJoinTMP is composed by : 6 Objects, within each a timePosted attribute (used for compare these different array Objects).
$scope.newJoin is an empty Array. I want to fill it with the Objects inside $scope.newJoinTMP but with the certainty to have once each Objects, and not twice the same ($scope.newJoinTMP can have duplicates Objects inside, but $scope.newJoin mustn't).
angular.forEach($scope.newJoinTMP, function(item)
{
angular.forEach($scope.newJoin, function(item2)
{
if (item.timePosted === item2.timePosted)
{
//snap.val().splice(snap.val().pop(item));
console.log("pop");
}
else
{
$scope.newJoin.push(item);
console.log("newJoin :", $scope.newJoin);
}
});
});
if(!$scope.newJoin.find(el=>item.timePosted===el.timePosted){
$scope.newJoin.push(item);
console.log("newJoin :", $scope.newJoin);
}
You dont want to push inside an forEach, as it will push multiple times...
There might be better ways to handle your particular situation but here's a fix for your particular code.
Replaced your inner for each with some which returns boolean for the presence of element and by that boolean value, deciding whether to add element or not
angular.forEach($scope.newJoinTMP, function(item)
{
var isItemPresent = $scope.newJoin.some(function(item2)
{
return item.timePosted === item2.timePosted;
//you dont need this conditional handling for each iteration.
/* if (item.timePosted === item2.timePosted)
{
//snap.val().splice(snap.val().pop(item));
console.log("pop");
}
else
{
$scope.newJoin.push(item);
console.log("newJoin :", $scope.newJoin);
} */
});
if( ! isItemPresent ) {
$scope.newJoin.push(item);
} else {
//do if it was present.
}
});
If you want to avoid the nested loop (forEach, some, indexOf, or whatever) you can use an auxiliar object. It will use more memory but you will spent less time.
let arr = [{ id: 0 }, { id:0 }, { id: 1}];
let aux = {};
const result = arr.reduce((result, el) => {
if (aux[el.id] === undefined) {
aux[el.id] = null;
return [el, ...result];
} else {
return result;
}
}, []);
console.log(result);
You can use reduce
$scope.newJoin = $scope.newJoinTMP.reduce(function(c, o, i) {
var contains = c.some(function(obj) {
return obj.timePosted == o.timePosted;
});
if (!contains) {
c.push(o);
}
return c;
}, []);
The problem with your current code is, if newJoin is empty, nothing will ever get added to it - and if it isnt empty, if the first iteration doesn't match the current item being iterated from newJoinTMP - you're pushing.
I have tagsList which has about 20 tags, and termIds which is an array of up to 3 tag ids.
I'm trying to find the tags that match the ids in termIds in the tagsList, then set their borders. Looking to avoid for loops and object-oriented programming in favor of a functional programming solution using Ramda curry.
A tag in tagsList looks like :
{
term: 'hi',
id: 123
}
And termIds could look like [123, 345, 678]
When I find an id that matches, I give that tag a new key border1:true, border2:true etc...
Goal:
There is a list of tags, I have another array of termIds, goal is to see if any of the tags in the tagsList have an id that matches the termIds. If so give it a border1, if there are 2, then the 2nd gets border2 and finally 3 gets border 3.
What I tried first:
const checkId = _.curry((term_id, tag) => {
if (tag.id === term_id) {
console.log('match found!', tag)
}
});
const matchId = checkId(termIds);
const coloredTags = R.map(matchId, tagsList);
console.log('coloredTags', coloredTags)
return tagsList;
However this did not work because I am preloading the entire termIds array into the checkId function. When instead I want to preload it with the individual items.
Next I tried this which I thought would work but getting a strange error:
const matchId = R.forEach(checkId, termIds);
This seems a reasonable approach:
R.map(tag => {
const index = R.indexOf(tag.id, termIds);
return (index > -1) ? R.assoc('border' + (index + 1), true, tag) : tag
})(tagsList);
//=> [
// {id: 123, term: "hi", border1: true},
// {id: 152, term: "ho"},
// {id: 345, term: "hu", border2: true},
// {id: 72, term: "ha"}
// ]
Although it could probably be made points-free with enough effort, it would likely be much less readable.
You can see this in action on the Ramda REPL.
If you want to make this into a reusable function, you can do it like this:
const addBorders = R.curry((terms, tags) => R.map(tag => {
const index = R.indexOf(tag.id, terms);
return (index > -1) ? R.assoc('border' + (index + 1), true, tag) : tag
})(tags))
addBorders(termIds, tagsList)
(The call to curry is a Ramda habit. It means you can call addBorders(termIds) and get back a reusable function that is looking for the tags. If you don't need that, you can skip the curry wrapper.)
This version is also on the Ramda REPL.
I think pure JS is enough to do it without Ramda. You just need a map :
var tagsList = [{term: 'hi', id: 123}, {term: 'ho', id: 152}, {term: 'hu', id: 345}, {term: 'ha', id: 72}];
var termIds = [123, 345, 678];
var i = 1;
var results = tagsList.map(x => {
if (termIds.indexOf(x.id) !== -1) x["border"+ (i++)] = true;
return x;
});
console.log(results);
Ah just figured it out, I had to curry the logic a 2nd time:
const matchId = R.curry((tag, term_id) => {
if (tag.id === Number(term_id)) {
console.log('match found!', tag)
}
});
const curried = R.curry((termIds, tag) => {
return R.map(matchId(tag), termIds);
});
const coloredTags = R.map(curried(termIds), tagsList);
console.log('coloredTags', coloredTags)
return tagsList;
So at the coloredTags line, a tag from tagsLists goes into the curried(termIds). Ramda functions accept params from right to left.
curried(termIds) is already preloaded with the termIds array. So next in the const curried = line, the termIds array and single tag make it in and the tag gets sent along into the next curried function matchId, also the termIds array is placed in the R.map. Ramda list functions accept the Array of data as the right param.
Finally in matchId I can make my check!
UPDATE
So the above answers the question I asked, about how to curry an item from an Array. However it caused a bug in my app. Since the termIds array could hold up to 3 items, the coloredTags R.map will run up to 3 times and create duplicate tags in my tagsList.
So just for completeness this is how I solved my in problem, much simpler and didn't need to use a double curried function.
const setTagColors = (tagsList, state) => {
const setBorder = (tag) => {
if (tag.id === Number(state.term_id_1)) {
tag.border1 = true;
} else if (tag.id === Number(state.term_id_2)) {
tag.border2 = true;
} else if (tag.id === Number(state.term_id_3)) {
tag.border3 = true;
}
return tag;
};
const coloredTags = R.map(setBorder, tagsList);
return state.term_id_1 ? coloredTags : tagsList;
};