I've been looking for a way to perform PCA on angular data in R and haven't succeeded yet.
I have a set of monitoring data for each of multiple plant species on the number of flowers opened at every 30 min (like 3 flowers opened at 0:00, 2 flowers at 0:30, 0 flowers at 1:00, ..., 5 flowers at 23:30). I want to reduce these time values to the 1st component from PCA (PC1) then use it as the responding variable of each plant species for the latter analyses.
I plan to convert time data to angles on a 24-h clock before analyses. Because my data are circular (or angular, directional, however you call it), I guess I cannot perform an ordinary PCA. I mean, 0:00 should be treated as a similar value with 23:30 even if their angles look different (0 and 352.5 degrees).
I would greatly appreciate if you could kindly give me a direction, thank you so much!