Select X# of variables from array at the furthest possible intervals.

Question

Ok, I've been working on this one for a while and I'm thinking I'm either missing something really stupidly simply because of it, or I've got my equation wrong still. 
Basically, what I'm trying to do is select X number of items out of an array.  The only catch is, these items need to be as far apart from each other as possible.  So for example, one time I might have an array with 93 items in it which I need to grab 36 of them, evenly spaced through the array (so the first one would be the first one in the array, and the last one would be the last in the array.
How would I go about telling the script to grab the correct array values (the most evenly spaced ones), ending up with only the X amount of output values?
Thanks!
dgolberg

Answer 1

Hmm, this is kind of a different perspective than what I was originally thinking, but it might work.  I'll have to test it out, though it would require me running the array twice; the first time picking out the specific ones and splicing them out of the array, the second simply grabbing the remainder.
To put it a little differently, what I was originally thinking is cycling through an array (this array's length and content varries depending on the input), and would grab the the "masters" out of the array at the set intervals (these intervals are where I'm having the most trouble), and anything it finds matching a set range for the current loop cycle that isn't considered a "master" is placed under the master as a "slave" (or essentially, a duplicate).  Below is an example of one of the loops I'm using (I have 3 nested loops in order to cycle through 3 "dimensions" of values) with my last attempt at this issue (which is only correct in certain ranges rather than all ranges like I need).
var DF = tA.length / mNum;  //tA.length is the array length, mNum is the number of masters desired from that array.  For example, array length of 100, mNum of 75; DF = 1.333333....
var master = 0;
for(var z=range[1];z<range[2]+2;z=z+5) { //Cycles through the array 5 units at a time (to speed up the script)... There are 2 other loops above this using the y and z variables seen in the if statements below.
     for(var i=0;i<tA.length;i++) { //Cycles through the tempArray to find matches to the current cycle of the above loops, +/- 2
           if(tA[i][0] <= x + 2 && tA[i][0] >= x - 2 && tA[i][1] <= y + 2 && tA[i][1] >= y - 2 &&tA[i][2] <= z + 2 && tA[i][2] >= z - 2 && master < 1) { //Checks for a match, and if the master is less than 1, it sets the match as a master.
               master = master + DF; //Adds the DF (short for Dupe Frequency) to the current master number.
               outArray.push(tA[i]); //Set the match as a master
          } else if(tA[i][0] <= x + 2 && tA[i][0] >= x - 2 && tA[i][1] <= y + 2 && tA[i][1] >= y - 2 &&tA[i][2] <= z + 2 && tA[i][2] >= z - 2 && master >= 1) { //Checks for a match, and if the master is greater than 1, it sets a duplicate.
               master = master - 1;
               outArray[outArray.length-1].push(tA[i][3]); //Set the match's name as a slave under the last master
Basically, using the code above; I need it to somehow (while cycling through the tA.length loop), figure out how often it should grab either a slave or a master (depending on which there are more of), and then the next X number of matches are either a master or a slave (again, depending on which there are more of).  So, for example, if there are 25 masters, out of 100 total items in the array, it would pick one master, the next 3 matches would be slaves, and then it would pick another master, 3 more slaves, etc. etc.  Where things start getting out of whack is when the intervals start ending up in fractions (say every 1.5 is a slave).  Obviously, you can't grab half of one, so you'd need to do a pattern more like: 1 master, 1 slave, 1 master, 2 slaves, 1 master, 1 slave; etc.
The part I'm having trouble with is getting a working equation that knows how often to pick the (in the example above) slaves based on this varying pattern, and do so accurately regardless of the array length to master/slave ratio (the above method seems to get further off as the mNum gets closer to the tA.length).
I guess, more than anything really, I'm just having trouble getting the math to work out right as I'm apparently using the wrong equation in my code.  If anyone has any ideas though, let me know.