Merge pull request #7 from akey7/issue_002_cos_sum

Issues 002 and 003

DESCRIPTION

@@ -1,15 +1,18 @@
 Package: fftpipe
 Type: Package
-Title: What the Package Does (Title Case)
+Title: A Pipeable Interface to Base R's fft() Function
 Version: 0.1.0
-Author: Who wrote it
-Maintainer: The package maintainer <[email protected]>
-Description: More about what it does (maybe more than one line)
-    Use four spaces when indenting paragraphs within the Description.
+Author: Alicia M. F. Key
+Maintainer: Alicia M. F. Key <[email protected]>
+Description: fftpipe wraps dataframes, piping, and the tidyverse around base R's fft() function.
+    fftpipe's style and interface are inspired by tidyverse and tidymodels. This package contains functions for generating, transforming, and plotting waveforms with operations around the fft() function.
 License: What license is it under?
 Encoding: UTF-8
 LazyData: true
 Suggests: 
     testthat (>= 3.0.0)
 Config/testthat/edition: 3
 RoxygenNote: 7.2.3
+Config/testthat/parallel: true
+Imports: 
+    dplyr

R/cos_sum.R

@@ -0,0 +1,26 @@
+cos_sum <- function(incoming, freqs, amplitudes = NULL, phases = NULL) {
+  stopifnot("incoming waveform must a data.frame." = is.data.frame(incoming))
+  stopifnot("freqs must be a vector of doubles or a single double." = is.numeric(freqs))
+
+  if (is.null(amplitudes)) {
+    amplitudes <- rep(1.0, length(freqs))
+  }
+
+  if (is.null(phases)) {
+    phases <- rep(0.0, length(freqs))
+  }
+
+  sr <- length(incoming$.sec) / tail(incoming$.sec, n = 1)
+
+  waveform_matrix <- matrix(nrow = length(freqs) + 1, ncol = nrow(incoming))
+  waveform_matrix[1, ] <- incoming$.value
+
+  for (i in seq_along(freqs)) {
+    freq <- freqs[i]
+    amplitude <- amplitudes[i]
+    phase <- phases[i]
+    waveform_matrix[i + 1,] <- amplitude * cos(2 * pi * freq * incoming$.sample / sr)
+  }
+
+  dplyr::mutate(incoming, .value = colSums(waveform_matrix))
+}

tests/testthat/test-cos_sum.R

@@ -0,0 +1,11 @@
+test_that("cos_sum() stops when invoked bad arguments.", {
+  expect_error(cos_sum(5, 5))
+})
+
+test_that("cos_sum() creates the sum of a single cosine.", {
+  result <- fftpipe::waveform(duration_s = 1.0, sr = 10) %>%
+    cos_sum(1)
+
+  .value <- c(0.809017, 0.309017, -0.309017, -0.809017, -1.000000, -0.809017, -0.309017, 0.309017, 0.809017, 1.000000)
+  expect_identical(round(.value, 5), round(result$.value, 5))
+})