Split a matrix in quintile based on ascending order

Hello,

I have a matrix of 2874x26 that I'd like to split into quintile for each of the 26 years. I've tried the quantile function many times but I can't figure out a way to do this at once.

Best regards,

Frank

[Francis Chabot]

Note that there's some NaN in my matrix and I want to exclude them when forming my quintile for each year.