Parsing time-strings in Javascript

Question

So, I have this web server that parses an XML-file with a certain 'time-period'.

The time-period is presented as follows (I can't change this):

00:05:00 00:09:15 01:13:15 in an HH:MM:SS format.

I want to do an _.filter() select on all objects with a date between for instance 00:00:00 and 00:10:00, and then a filter with all objects between 00:10:00 and 00:20:00.

EDIT (clarification): With the time periods are 'times watched'. Let's say there are 50 entries of the time period, ranging from 00:00:00 to 1:30:00, but I want to make a new list that contains

• The time period
• The average 'times watched' in that time period.

This means I need some way to say: 'Select all time periods between zero minutes and 10 minutes. Give me a list of those. Compute the mean'.

For that, I would need to have some possibility to do arithmetic operations, seeing I would like to

• Compare dates
• Add 10 minutes on each iteration

However, the Javascript Date object doesn't seem to handle 'just times' that well, neither does the moment.js library. How would I go for this?

Answer 1

Here is how I would do in JS:

times=['00:05:00', '00:09:15', '01:13:15'];

1. First get seconds

   function getsec(time){
     arr=time.split(':');
     return (+arr[0])*3600 + (+arr[1])*60 + (+arr[2]);
   }
   
   times.map(getsec)
   [ 300, 555, 4395 ]
   

2. Then filter times into slots of particular time period

   function filter(last, curr, index, array){
     chk=parseInt(curr/600); //slots for 10 minutes
     if (typeof last[chk] === 'undefined')
     {
       last[chk]=[];
       last[chk].push(curr);
     }
     else
       last[chk].push(curr);
     return(last)
   }
   
   times.map(getsec).reduce(filter,[]);
   [ [ 300, 555 ], , , , , , , [ 4395 ] ]
   

   Returns array of arrays. Each child array contains times within slots in increasing order

3. Calculate mean

   function avg(last, curr, index, array){
     if(index==array.length-1)
     return (last+curr)/array.length;
     else
     return last+curr;
   }
   
   times.map(getsec).reduce(avg,0);
   1750
   
   function getavg(arr){
     return arr.reduce(avg,0);
   }
   
   times.map(getsec).reduce(filter,[]).map(getavg);
   [ 427.5, , , , , , , 4395 ]
   

   Since we are dealing with array of arrays we need a wrapper.

Finally I would say that if you have many entries, databases would be faster.