This can be rather difficult for general data where an explicit equation isn't obvious (even though it'll work quite often as pointed out by johncolanduoni below).
[I think it's neat that] for sufficiently smooth and periodic data, a Fourier transform will do exactly this (decompose a function into its even and odd parts)!
[I think it's neat that] for sufficiently smooth and periodic data, a Fourier transform will do exactly this (decompose a function into its even and odd parts)!