Best way to handle an array and nested loops

Hey guys,

I'm struggling with an array and nested loops and wanted to bounce it off the community.

What I need to do is take an array of >50000 values and loop through it.

The first thing I need to do is capture the year of the value and group together all the values that have the same year

The second thing I need to do is for each year, group those into months

The third thing I need to do is average out the values in each month (easy part)

I was thinking something similar to:

year = array[0].year; 

for(int i = 0; i < array.length; i++)
{
    if(year == array[i].year)
    {
         month = array[i].month;
         while(month = array[i].month)
         {
               average the values and collect into another array
         }
         month = array[i].month
    }
    else
    {
         year = array[i].year
     }
}

But I dunno...the logic in my brain tells me this isn't gonna work and values are going to get skipped. I can't say "I'll just collect them into separate arrays" because that isn't extensible.

I can't hard code anything because I don't know what data is going to run through it once it's built but I'm seriously stuck here.

Can anyone give me some guidance here?

Thanks! <3