Javascript, basic associative array

Question

I have a simple string and i split it into an array:

var alphabet = "a,b,c,d,e";
var letters = alphabet.split(",");

var dict = [];
for ( var i = 0; i < letters.length; i++ ) {
    dict[ letters[i] ] = true;
}

What stumps me is that when i do a

console.log(dict[letters[0]] +"|"+ dict["a"]);

I get

//true|undefined

I dont understand the difference between letters[0] and "a". And i'm absolutely sure that letters[0] and "a" are both type of string.

EDIT: I just tried changing variable "dict" from the square brackets to the curly ones but it still gives me undefined.

EDIT 2: The below code is what im working with. "dictionary.txt" is a text file containing some 90k words separated by "\n". In this text file, the letter "a" is on the first line.

$.get( "tiles/dictionary.txt", function( txt ) {
// Get an array of all the words
var words = txt.split( "\n" );
// And add them as properties to the dictionary lookup
// This will allow for fast lookups later
for ( var i = 0; i < words.length; i++ ) {
    dict[ words[i] ] = true;
}
console.log(dict[words[0]]+"|"+dict["a"]);
});

Maybe i should have just started out with this, instead of trying to make a simplified version of it.

My local Node.JS and the JSFiddle created by @Ajwhiteway both work as written, so it's not the code. What implementation of JS are you using? — Mark Reed
– Mark Reed, Commented Dec 10, 2015 at 19:53
@MarkReed hi Mark please see my EDIT 2, thank you. I am not sure what JS im using, but im on Netbeans 8.0.2 — Vibol
– Vibol, Commented Dec 10, 2015 at 20:05
So none of the lines of the file is just a. Perhaps there is whitespace besides the newline? — Mark Reed
– Mark Reed, Commented Dec 10, 2015 at 20:09
add 1 line to your test code both version console.log(words[0] == "a") — HopefullyHelpful
– HopefullyHelpful, Commented Dec 10, 2015 at 20:12
@HopefullyHelpful huh interesting, I didnt think to test that. It turns out to be false. — Vibol
– Vibol, Commented Dec 10, 2015 at 20:15

Mark Reed · Accepted Answer · 2015-12-11 16:14:04Z

5

The problem is that your text file has carriage returns. Splitting on newline ("\n") doesn't remove the carriage returns, so the first element of the array is not "a" but "a\r". If you modify your code to the following, it should work, as it does in this fiddle:

$.get("https://dl.dropboxusercontent.com/u/16966255/dictionary.txt",
      function(txt) {
        var words = txt.split("\r\n");
        var dict = {};
        for (var i = 0; i < words.length; i++) {
          dict[ words[i] ] = true;
        }
        alert(dict[words[0]]+"|"+dict["a"]);
      });

Instead of requiring the file to contain carriage returns, you could split with a regular expression that matches whether it does or not:

var words = txt.split(/\r?\n/);

But if you plan on using a much larger file, note that splitting with a regex is noticeably less efficient than splitting with a constant string.

Also, while I have changed the initialization of dict from [] to the more standard {}, that was not the problem; an Array is just a particular type of Object, and every Object in Javascript is really an associative array.

edited Dec 11, 2015 at 16:14

answered Dec 10, 2015 at 19:46

Mark Reed

96k17 gold badges149 silver badges189 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Felix Kling Over a year ago

"every Object in Javascript is really an associative array" I wouldn't say that. Objects are more like dictionaries or maps. "Associative array" implies a certain order of the elements, which is not the case for object properties. Actually, any comparison of objects to another data structure is probably wrong.

Filipe Merker Over a year ago

@Mark-reed You're goddamn right. IF you type typeof [] you will see "object".

Mark Reed Over a year ago

@FelixKling No, "associative array" does not imply ordering of elements; it is synonymous with "dictionary" or "map" in those senses. PHP is probably the best-known implementation that actually calls them "associative arrays", and its are ordered, but that is not at all implied by the name.

Felix Kling Over a year ago

Fair enough... I won't venture deeper because it only gets more confusion (en.wikipedia.org/wiki/Array_data_structure vs en.wikipedia.org/wiki/Array_data_type, etc)

Jeff Over a year ago

Ahh, you have satisfied my curiosity. This is the correct answer. +1

|

Jeff · Accepted Answer · 2015-12-10 19:46:23Z

3

Your dict var needs to be an object, not an array. In JavaScript, associative arrays are JSON objects.

var dict = {}; // Curly braces, not square brackets.

for ( var i = 0; i < letters.length; i++ ) {
    dict[ letters[i] ] = true;
}

console.log(dict[letters[0]] +"|"+ dict["a"]);

You will get

// true|true

edited Dec 10, 2015 at 19:46

answered Dec 10, 2015 at 19:42

Jeff

2,0682 gold badges16 silver badges18 bronze badges

3 Comments

Mark Reed Over a year ago

It's more conventional to use the object literal syntax {}, but it absolutely still works if you use the array literal syntax [] instead. Try before dismissing..

Jesse Kernaghan Over a year ago

@MarkReed while it technically 'works', it is just adding keys to the array object, not adding array items. The length is 0, and iterating on it will cause some unexpected results. It should be an object literal.

Mark Reed Over a year ago

It's not best-practice, but it doesn't explain the problem seen in the question.

Ajwhiteway · Accepted Answer · 2015-12-10 19:43:51Z

2

I ran your code as it on JSFiddle and it logged true|true. You could try changing

dict = [];

to

dict = {};

on your local implementation to see if it corrects your problem.

answered Dec 10, 2015 at 19:43

Ajwhiteway

1,0061 gold badge11 silver badges23 bronze badges

Comments

Phil Dornfeld · Accepted Answer · 2015-12-10 19:42:49Z

-2

Javascript doesn't support associative arrays. If you declare it with [], all indexes must be numbers.

answered Dec 10, 2015 at 19:42

Phil Dornfeld

1054 bronze badges

Collectives™ on Stack Overflow

Javascript, basic associative array

4 Answers 4

6 Comments

3 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

3 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related