Construct javascript array from associative array and long string

Question

I have a javascript assoc array (object) like

aa = {"(one)":["a","b","c"], "(two)":["d","e","f"]}

and a string like

s = "(two) blah blah (one) etc (two)"

I want to turn the assoc array into a plain array whose order is as specified in the string

newarray = [["d","e","f"] , ["a","b","c"], ["d","e","f"]]

The only thing is, the array and string may contain many millions of items. If I do this using string.match with the global modifier, then iterating over the results, will I end up using huge amounts of memory? Is there a way to iterate over matches in the string without storing the text of all the matches (a bit like a iterator version of string.search)?

use string.split passing in a regular expression to split by the (one),(two) etc, perhaps? Then just iterate through the array returned to build your newarray? — PulseLab
– PulseLab, Commented Jun 9, 2014 at 9:15
@adeneo, I was using "assoc array" as shorthand. It's all hashed storage anyway. — user2667066
– user2667066, Commented Jun 9, 2014 at 9:18
@PulseLab thanks, but won't that end up storing huge numbers of extra strings. Or does string.split do compiler magic so that new substrings are actually created, just providing a "view" into the original static string that can be iterated over? — user2667066
– user2667066, Commented Jun 9, 2014 at 9:23

Robby Cornelissen · Accepted Answer · 2014-06-09 09:56:11Z

1

I'm thinking something along these lines, based on a regular expression:

var aa = {"(one)":["a","b","c"], "(two)":["d","e","f"]};
var s = "(two) blah blah (one) etc (two)";
var result = [];

s.match(/(\(.+?\))/g).forEach(function(match) {
    result.push(aa[match]);
});

answered Jun 9, 2014 at 9:56

Robby Cornelissen

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3 Comments

user2667066 Over a year ago

Ideal, if s.match().forEach is optimised by the compiler to act as an iterator, rather than having to store an intermediate array of all the matches. I suspect it is optimised like this. Will try. Thanks!

Robby Cornelissen Over a year ago

Yeah not sure about that optimization... Depends on the Javascript engine, but not sure if any of them would optimize it this way. If not, you could use RegExp.exec() to do progressive matching.

user2667066 Over a year ago

Aha - I didn't spot that RegExp.exec() did progressive matching (docs). That's probably just what I need. Thanks.

Dastagir · Accepted Answer · 2014-06-09 09:49:52Z

1

var aa = {"(one)":["a","b","c"], "(two)":["d","e","f"]};
var s = "(two) blah blah (one) etc (two)"
var newarray = [];
var res = s.match(/\((.*?)\)/g);
var i = 0;
while (i < res.length){
    newarray.push(aa[res[i]]); 
    i++;
}
console.log(newarray);

Finally this one works perfectly.

http://jsfiddle.net/KRzRj/

edited Jun 9, 2014 at 9:49

answered Jun 9, 2014 at 9:24

Dastagir

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5 Comments

Robby Cornelissen Over a year ago

This does not take the string into account at all.

Robby Cornelissen Over a year ago

Sorry, too fast with my comment. Didn't realize you were still editing. Solution still doesn't look correct though...

user2667066 Over a year ago

That will construct an array in the order returned by the for(key in aa) call. On my machine that returns (one) first, then (two), so it gets the order wrong (newarray = [["a","b","c"], ["d","e","f"] , ["d","e","f"]])

Dastagir Over a year ago

@user2667066 I did some edit and the answer is now exactly what your looking for [["d","e","f"] , ["a","b","c"], ["d","e","f"]]

user2667066 Over a year ago

But that still stores an intermediate array in res. See my comment above, I think progressive RegExp.exec is what I need.

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