Efficient parsing of a string into float array in JavaScript

If you prefix your string with one space, you can use this to get the first number out of the string:

var start = 0 // Initial search offset.
var firstOccurence = input.indexOf(' ', start);
//Get the substring from the first occurrence of ' ' after start, to the next one, and parse it as a float.
parseFloat(input.substring(firstOccurence , input.indexOf(' ', firstOccurence+1)));

Then, you can use the following to get the numbers after that, out of the string:

firstOccurence = t.indexOf(' ', firstOccurence+1);
parseFloat(t.substring(firstOccurence , t.indexOf(' ', firstOccurence+1)));

Using this in a loop, you can search through your list, and you can start searching the list at a specified index. You can't however, ask for the 7th float in the list, for example. The only reliable way to do that is to use .split(' '), or to use the above code in a loop.

To find the nth float in the input, you can use the following:

for(var i = 0, previousIndex = 0; i < n; i++){
    previousIndex = input.indexOf(' ', previousIndex + 1);
}
var float = parseFloat(input.substring(previousIndex, input.indexOf(' ',  previousIndex + 1)));

This function can handle multiple white spaces as well as input that does not parse as a float.

input = "123 123 123  foo", start = 0, end = 0, result = [], num;

// empty string evaluates to false
while( end < input.length ) {
    end = input.indexOf(" ", start );
    // -1 => only one element in input || end of the string has been reached
    if( end === -1 ) { end = input.length }
    num =  parseFloat( input.substring( start, end ) );
    // Should extracted string fail to parse then skip
    if( num ) result.push( num ); 
    // move forward or end will match current empty space
    start = end + 1;
}

result[2] // => "123";

Fiddle here

UPDATE

Just had a brainwave. Don't use the map function but just use the array created by splitting the string like so:

var floats = input.split(' ');
for( var i = 0, len = input.length; i < len; i++ ) {
    input[i] = parseFloat( input[i] );
}

How about this?

parseFloat(input.substring(5,10));

Where 5,10 are the starting and ending offsets of your desired chunk of string.