Ensures that each time stamp is unique by averaging all rows within duplicated time stamp values (for rotation columns: circular mean). Also adds a column `n` which is the count of rows for this time stamp. This is useful because there can be several observations for a time stamp in a movement data frame. One reason is that the epoch can be "frozen" when the menu button is pressed, generating new data but freezing the timer.

summarise_movement(df, by)

Arguments

df

Movement data frame

by

= "time": time stamp key