Issue #11

Create compute_fft(), its documentation, and its tests.

NAMESPACE

@@ -1,6 +1,7 @@
 # Generated by roxygen2: do not edit by hand
 
 export("%>%")
+export(compute_fft)
 export(cos_sum)
 export(exp_decay)
 export(length_norm)
@@ -12,4 +13,5 @@ importFrom(ggplot2,geom_line)
 importFrom(ggplot2,ggplot)
 importFrom(ggplot2,labs)
 importFrom(magrittr,"%>%")
+importFrom(stats,fft)
 importFrom(utils,tail)

R/compute_fft.R

@@ -0,0 +1,25 @@
+#' compute_fft()
+#'
+#' Computes the FFT of the given waveform.
+#'
+#' @param incoming data.frame containing the incoming waveform for the FFT.
+#'
+#' @return A data.frame with the following columns: .values with the values from the FFT, and .idx with the indexes for these values (this makes it easier to plot with ggplot later).
+#' @export
+#' @importFrom stats fft
+#'
+#' @examples
+#' waveform(duration_s = 1.0, sr = 10) %>%
+#'   cos_sum(freqs = c(2.0, 3.0), amplitudes = c(0.5, 1.0)) %>%
+#'   length_norm() %>%
+#'   compute_fft()
+compute_fft <- function(incoming) {
+  stopifnot("incoming must be a data.frame with a waveform." = is.data.frame(incoming))
+
+  .value <- stats::fft(incoming$.value)
+
+  data.frame(
+    .idx = seq_along(.value),
+    .value = .value
+  )
+}

tests/testthat/test-compute_fft.R

@@ -0,0 +1,21 @@
+test_that("compute_fft() expects a data.frame", {
+  expect_error(compute_fft(1.0))
+})
+
+test_that("compute_fft() computes an FFT of the sum of two cosines", {
+  wv <- waveform(duration_s = 1.0, sr = 10) %>%
+    cos_sum(freqs = c(2.0, 3.0), amplitudes = c(0.5, 1.0)) %>%
+    length_norm()
+
+  actual <- compute_fft(wv)$.value
+
+  expected <- c(
+    -4.857226e-17+0.000000e+00i, 0.000000e+00-8.326673e-17i,
+    7.725425e-02+2.377641e-01i, -1.545085e-01+4.755283e-01i,
+    -5.551115e-17+5.551115e-17i, -8.326673e-17+2.775558e-17i,
+    -5.551115e-17-5.551115e-17i, -1.545085e-01-4.755283e-01i,
+    7.725425e-02-2.377641e-01i, 0.000000e+00+5.551115e-17i
+  )
+
+  expect_equal(expected, actual, tolerance = 1e-3)
+})