edit: don't do this. this was a stupid way of doing something I tried when I was new to programming
I have a list of 32 pieces of data in an array that are paired like this
"foo:bar","baz:example","cat:dog"
and I want to loop through that array to and stop on the pair that matches the user's input. So, for example, if the user types in "foo" it'll return both "foo" and "bar" separately, and if the user types in "bar" it'll return both "foo" and "bar". There are no values that repeat.
Right now what I have is a huge table with if statements. So if the user's input is x, then it returns the correct value. I had to do the matching by hand, and I'm assuming that looping through the array until the correct value is found would be more efficient than 64 different ifs.
I've tried something like this (just an example) using two separate arrays:
for (var i=0;i<array.length;i++) {
if (array[i] === user_input) {
var index = indexOf(array[i]);
break;
}
}
and then using the index variable as the index number of the value in each array, but it returns undefined
I've also tried this: Separate key and value pairs into two arrays
But it gives me all the values in the array, which I don't want. I just want one specific value that the user inputs. And while I can select one specific portion of the array using the index number, I can't figure out how to make that dynamic (e.g. changing based on what the user inputs).
Is it even possible to do this? And if not, what would be the best way?
Thanks.
You can do this:
function getPair(arr, search) {
var rtn = arr.filter(function (v, i) {
return new RegExp("\\b" + search + "\\b").test(v);
})[0];
return rtn ? rtn.split(':') : -1;
}
Use it like this:
var array = ["foo:bar","baz:example","cat:dog"];
getPair(array, "foo"); // ["foo","bar"]
Note: The above function returns -1 if the search string isn't found in the array.
Here's a function that iterates over the array, and checks if the user_input is anywhere. If so, it will return the string that it found a match for.
function getPair(array, user_input) {
for (var i=0;i<array.length;i++) {
var pair = array[i].split(':');
if (pair.indexOf(user_input) >= 0) {
return pair;
}
}
return [];
}
var array = ["foo:bar","baz:example","cat:dog"];
getPair(array, "foo"); //will return ['foo', 'bar']
getPair(array, "bar"); //will return ['foo', 'bar']
getPair(array, "dog"); //will return ['cat', 'dog']
getPair(array, "zzz"); //will return []
I would suggest to work with objects. First, convert your array:
var pair,obj1={},obj2={};
for (var i=0;i<array.length;i++) {
pair=array[i].split(":");
obj1[pair[0]]=pair[1];
obj2[pair[1]]=pair[0];
}
This will give you the following objects:
obj1={
"foo":"bar",
"baz":"example",
"cat":"dog"
};
obj2={
"bar":"foo",
"example":"baz",
"dog":"cat"
};
Then based on the user input:
if (obj1[user_input]) {return [user_input,obj1[user_input]];}
else if (obj2[user_input]) {return [obj2[user_input],user_input];}
else return undefined;
Live demo: http://jsfiddle.net/x23qG/
Related
The condition is such that I have to enter a string to an array to a given position
such that all the pre position if not exist should be made to be empty strings.
example;
var array = []; // now I want to enter a string 'hello' at index 2
now the array should look like:
array = [ '','','hello']; //now lets say I want to enter a string 'world' at index 4
so the array should become:
array = [ '','','hello','','world'];
Is there a way to do this?
or do i have a better option to enter a string and and its position?
Please enlighten me.. :)
Something like this should do the trick. The function takes three arguments: the target array, the index (0-based) and the value. Just iterate from the finish of you array to the new position and add "" to each entry, then, after the loop, enqueue the desired string. Here's the fiddle.
let a = ['', '', 'Hello'];
function addStringAtPosition(
array,
key,
value
) {
for (let i = array.length; i < key; i++) {
array[i] = '';
}
array[key] = value;
}
addStringAtPosition(a, 5, 'World!');
First find out how many additional elements need to add ''
push these new elements to array.
push the required value at end.
PS: Assumed the index always higher than the array length. We can add conditions to cover those cases as well.
const insert = (arr, value, index) => {
arr.push(...new Array(index - arr.length).fill(""));
arr.push(value);
return arr;
};
const array = [];
insert(array, "hello", 2);
console.log(array);
insert(array, "world", 4);
console.log(array);
I am trying to understand how to implement the map method (rather than using a for loop) to check a string for palindromes and return boolean values for whether the mapped array elements reversed are the same as the original array elements. I cannot seem to understand the syntax of the map method. How do I get the map to function on each element in the original array? What is the value? Here is my working code, which is only logging a value of undefined:
function palindromeChecker(string) {
var myString = string.toLowerCase();
var myArray = myString.split(" ");
var newArray = myArray.map(function (item) {
item.split("").reverse().join("");
return newArray === myArray;
});
}
console.log(palindromeChecker("What pop did dad Drink today"));
Here is a link to the fiddle:
https://jsfiddle.net/minditorrey/3s6uqxrh/1/
There is one related question here:
Javascript array map method callback parameters
but it doesn't answer my confusion about the syntax of the map method when using it to perform a function on an array of strings.
The map method will literally 'map' a function call onto each element in the array, take this as a simple example of increasing the value of each integer in an array by 1:
var items = [1,2,3];
items.map(function(item) {
return item + 1;
});
// returns [2,3,4]
In your case, you are trying to use map to accept or reject a string if it's a palindrome, so a simple implementation might be:
var items = ['mum', 'dad', 'brother'];
items.map(function(item) {
return item.split('').reverse().join('') === item;
});
// returns [true, true, false]
I'm not 100% sure of your reasons for using map, because if you were trying to just filter the array and remove the strings that aren't palindromes, you should probably use the filter method instead, which works in the same way, but would remove any that return false:
var items = ['mum', 'dad', 'brother'];
items.filter(function(item) {
return item.split('').reverse().join('') === item;
});
// returns ['mum', dad']
In your case you are splitting a string first to get your array of characters; you may also want to make that string lower case and remove punctuation, so an implementation might be:
var string = 'I live at home with my Mum, my Dad and my Brother!';
var items = string.toLowerCase().replace(/[^a-z0-9-\s]+/, '').split(' ');
items.filter(function(item) {
return item.split('').reverse().join('') === item;
});
// returns ['i', 'mum', dad']
As mentioned in one of the comments on your question, you need to ensure you return a value from your function if you are using a separate function to perform the check, so this is how your function should look:
function checkPalindromes(string) {
var items = string.toLowerCase().replace(/[^a-z0-9-\s]+/, '').split(' ');
items.filter(function(item) {
return item.split('').reverse().join('') === item;
});
return items;
}
And you would call it using:
checkPalindromes('I live at home with my Mum, my Dad and my Brother!'); // ['i', 'mum', 'dad']
try something like this:
let str = 'hello';
let tab = [...str];
tab.map((x)=> {
console.log("|"+x+"|");
return x;
})
newArray should include reversed version of theall items in myArray. After that, newArray should be reversed and joined with space in order to get the reversed version of the input string.
Here is the code:
function palindromeChecker(string) {
var myString = string.toLowerCase();
var myArray = myString.split(" ");
var newArray = myArray.map(function (item) {
return item.split("").reverse().join("");
});
console.log(newArray);
return newArray.reverse().join(" ") === string;
}
console.log(palindromeChecker("dad did what"));
Javascript map method on array of string elements by using split() function.
let str = 'hello';
str.split('').map((x)=> {
console.log("|"+x+"|");
return x;
})
Map is a higher-order function available in ES5. I think your newArraywill contain an array of boolean values.
In essence, map will iterate over every value in your array and apply the function. The return value will be the new value in the array. You can also use map and save the information you need somewhere else, and ignore the result of course.
var arr = [1,2,3,4];
var newArray = arr.map(function(i) {
return i * 2;
});
//newArray = [2,4,6,8]
The map function in javascript (and pretty much in any language) is a great little function that allows you to call a function on each of the items on a list, and thus changing the list itself.
The (anonymous) function you're passing as an argument accepts an argument itself, which is filled by an item of the list it is working on, each time it is called.
So for a list [1,2,3,4], the function
function(item) { return item + 1 }, would give you a list of [2,3,4,5] for a result. The function you passed to $.map() is run over each element of the list, and thus changing the list.
So for your code: in the function you're passing as an argument to $.map(), you're returning whether the old and new array are equal (which is false btw). So since you're returning a boolean value, the list you'll end up with is a list of bools.
What I think you want to do, is extract the newArray == myArray from the function you're passing to $.map(), and putting it after your $.map() call.
Then inside the function you're passing to $.map(), return the item you're splitting and whatnot, so your newArray will be an array of strings like myArray.
Apart from a few minor mistakes in your code, such as scope issues (you're referencing the "newArray" and "myArray" outside of the function in which they where defined, and therefore, getting "undefined")..
The main issue you had is that you addressed the ENTIRE array inside the map function, while the whole concept is breaking things down to single elements (and then the function collects everything back to an array for you).
I've used the "filter" function in my example, because it works in a similar manner and I felt that it does what you wanted, but you can change the "filter" to a "map" and see what happends.
Cheers :)
HTML:
<body>
<p id="bla">
BLA
</p>
<p id="bla2">
BLA2
</p>
</body>
Javascript:
function palindromeChecker(string) {
var myString = string.toLowerCase();
var myArray = myString.split(" ");
var newArray = myArray.filter(function (item) {
var reversedItem = item.split('').reverse().join('');
return item == reversedItem;
});
document.getElementById("bla").innerHTML = myArray;
document.getElementById("bla2").innerHTML = newArray;
}
palindromeChecker("What pop did dad Drink today");
Thanks for your input, all. This is the code I ended up with. I fixed the scope issues in the original post. My main problem was understanding the syntax of the map method. In particular, I could not understand from other online resources how to determine the value in the callback function. So, with much help from above I have placed the map method inside the palindromeChecker, and done all of the work on the array inside the map function.
var palindromeChecker = function(string) {
var newString = string.toLowerCase().split(' ');
newString.map(function(item) {
console.log(item.split('').reverse().join('') === item);
});
};
palindromeChecker("What pop did dad drink today");
//Returns false, true, true, true, false, false
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.
I have some data that I'm trying to clean up. For the field in question, I know what the possible values are, but the value is stored in a concatenated string and I need them in an array. Here is what I would like to do:
var valid_values = ['Foo', 'Bar', 'Baz'];
var raw_data = ['BarFoo','BazBar','FooBaz'];
desired_result = [['Bar','Foo'],['Baz','Bar'],['Foo','Baz']];
I'm not sure what this is called, so I hope this isn't a duplicate.
You can iterate over each data value, searching for allowed string with indexOf or contains and returning successful matches as array.
Here's my version of code and working example at jsFiddle:
var out = raw_data.map(function (raw) {
return valid_values.filter(function (value) {
return raw.contains(value);
});
});
//out === [['Bar','Foo'],['Baz','Bar'],['Foo','Baz']];
I assumed that output match order isn't important.
This is assuming some things about your data:
you need to split strings into 2-item pairs
input & terms are case-sensitive
you won't be dealing with null/non-conforming inputs (requires more edge-cases)
In that case, you'd want to do something like this:
// for each item in the desired result, see if it's a match
// at the beginning of the string,
// then split on the string version of the valid value
function transform(input){
for(i = 0; i < len; i++) {
if (input.indexOf(valid_values[i]) === 0) {
return [ valid_values[i], input.split(valid_values[i])[1] ];
}
}
return [];
}
// to run on your input
var j = 0, raw_len = raw_data.length, desired_result = [];
for(; j < raw_len; j++) {
desired_result.push(transform(raw_data[j]));
}
This code is pretty specific to the answer you asked though; It doesn't cover many edge cases.
I am trying to set up an array in jQuery and I then need to do a for loop on it. But it seems that I cant use an associative array for some reason?
var items = new Array();
items['foo'] = 123456;
items['bar'] = 789012;
items['baz'] = 345678;
items['bat'] = 901234;
alert(items.length);
This is just a test, but it return 0?
You can't make associative array in JavaScript like what you want, instead you can use Object.
For example:
var items = {
foo : 123456,
bar : 789012,
baz : 345678,
bat : 901234
}
And to calculate the length you can do:
var getObjectSize = function(obj) {
var len = 0, key;
for (key in obj) {
if (obj.hasOwnProperty(key)) len++;
}
return len;
};
Use: getObjectSize(items); // output: 4
For more see here.
Another one is:
Object.keys(items).length;
But not supported by all browsers.
var items = new Array();
items['foo'] = 123456;
The problem lies in the very first line. You believe that you are adding an item to the array at the index foo, but you are actually adding a property to the items variable with a key foo and value 123456. If you were to type items.foo it would give you back your 123456.
The problem with this approach is that adding a property to an array does not magically increase it's length.
If you want to have non-numeric indexes, you need to use an object instead of an array:
var items = {
foo: 123456,
bar: 789012,
baz: 345678,
bat: 901234
};
Another approach might be to set up two different arrays, which you construct in parallel:
var items = [], items2 = [];
items.push('foo');
items2.push(123456);
// etc.
alert(items2.length);
The efficiency of this approach depends on how you'll use it. If you're only going to loop through the list of items and do something to each of them, this approach may be more efficient. But if you need to use it like an associative array (items['foo']), then you're better off building an object.
The .length property returns the highest numerical index of the array. Thus, in your case, there is no numerical index and it returns 0. Try
items[98] = "something";
items.length will be 98..! Use the .length property with caution, and if you also want to count the non-numerical indici, loop over the Object (an Array is also an Object) and count its ownProperties.