In R stats::fft() is a function to perform the discrete Fourier transform (DFT) for a given array by a fast Fourier transform (FFT). It can also do the (unnormalized) inverse if given inverse = TRUE. In fact,
x <- runif(100)
all.equal(as.complex(x), fft(fft(x), inverse = TRUE)/length(x))
returns TRUE.
There is another useful variant called stats::mvfft(). This function accepts a matrix and just applies fft() to each column of it (but in a more efficient way). In other words,
y <- matrix(runif(1000), nrow = 100)
all(mvfft(y) == apply(y, 2, fft))
returns TRUE.