Calculate The Quartiles With The Condition Of The Year Or The Month Or Even Both

i have a dataset which is like a timeseries with 3 columns
first is year second month third values
so lets say like this

year month day value
2004 12 29 100
2004 12 30 200
2004 12 31 300
2005 01 01 50
2005 01 02 60
.....

I need to calculate the quartiles with the condition of the year or the month or even both... I suppose i need something like an array but i couldnt make it work untill now.