fst bearing to group centroid

R/bearing_to_group_centroid.R

@@ -0,0 +1,28 @@
+#' Calculate absolute bearing to group centroid
+#'
+#' @param DT expects group_mean columns generated with group_centroid
+#' @param coords character vector of column names for x, y
+bearing_to_group_centroid <- function(DT, coords = NULL) {
+  pre <- 'group_mean_'
+
+  stopifnot(length(coords) == 2)
+
+  xcol <- first(coords)
+  ycol <- last(coords)
+  group_xcol <- paste0(pre, xcol)
+  group_ycol <- paste0(pre, ycol)
+
+  stopifnot(xcol %in% colnames(DT))
+  stopifnot(ycol %in% colnames(DT))
+  stopifnot(group_xcol %in% colnames(DT))
+  stopifnot(group_ycol %in% colnames(DT))
+
+  DT[, bearing_centroid := fifelse(
+    .SD[[xcol]] == .SD[[group_xcol]] &
+      .SD[[ycol]] == .SD[[group_ycol]],
+    NaN,
+    atan2(.SD[[group_ycol]] - .SD[[ycol]],
+          (.SD[[group_xcol]] - .SD[[xcol]]))
+  )]
+  return(DT[])
+}