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#' Place nodes on a line or circle
#'
#' This layout puts all nodes on a line, possibly sorted by a node attribute. If
#' `circular = TRUE` the nodes will be laid out on the unit circle instead.
#' In the case where the `sort.by` attribute is numeric, the numeric values
#' will be used as the x-position and it is thus possible to have uneven spacing
#' between the nodes.
#'
#' @param graph An `tbl_graph` object
#'
#' @param circular Logical. Should the layout be transformed to a circular
#' representation. Defaults to `FALSE`.
#'
#' @param sort.by The name of a node variable to sort the nodes by.
#'
#' @param use.numeric Logical. Should a numeric sort.by attribute be used as the
#' actual x-coordinates in the layout. May lead to overlapping nodes. Defaults
#' to FALSE
#'
#' @param offset If `circular = TRUE`, where should it begin. Defaults to
#' `pi/2` which is equivalent to 12 o'clock.
#'
#' @param weight A weight for each node. Nodes will be spread out according to
#' their weight so that nodes with heigher weight will have more space around
#' them. Ignored if `use.numeric = TRUE`
#'
#' @return A data.frame with the columns `x`, `y`, `circular` as
#' well as any information stored as node variables in the tbl_graph object.
#' Further, if `circular = FALSE` a `width` column and if `circular = TRUE` a
#' `start`, `end`, and `r0` column.
#'
#' @family layout_tbl_graph_*
#'
#' @importFrom igraph gorder
#'
layout_tbl_graph_linear <- function(graph, circular, sort.by = NULL, use.numeric = FALSE, offset = pi / 2, weight = NULL) {
sort.by <- enquo(sort.by)
sort.by <- eval_tidy(sort.by, .N())
weight <- enquo(weight)
weight <- eval_tidy(weight, .N())
if (use.numeric && !is.null(weight)) {
cli::cli_warn('Ignoring {.arg weight} when {.code use.numeric = TRUE}')
}
weight <- weight %||% rep(1, gorder(graph))
if (length(weight) != gorder(graph)) {
cli::cli_abort('{.arg weight} must match the order of the graph')
}
if (any(weight < 0)) {
cli::cli_abort("{.arg weight} must be positive")
}
if (!is.null(sort.by)) {
if (length(sort.by) != gorder(graph)) {
cli::cli_abort('{.arg sort.by} must match the order of the graph')
}
if (is.numeric(sort.by) && use.numeric) {
x <- sort.by
weight <- 0
} else {
x <- c(0, cumsum(weight[order(sort.by)]))
x <- (x[-1] + x[-length(x)]) / 2
x <- x[order(order(sort.by))]
}
} else {
x <- c(0, cumsum(weight))
x <- (x[-1] + x[-length(x)]) / 2
}
nodes <- data_frame0(x = x, y = 0, width = weight)
if (circular) {
full_width <- sum(nodes$width)
if (full_width > 0) {
nodes$start <- 2 * pi * (nodes$x - nodes$width / 2) / full_width
nodes$end <- 2 * pi * (nodes$x + nodes$width / 2) / full_width
} else {
full_width <- max(nodes$x)
nodes$start <- 2 * pi * nodes$x / full_width
nodes$end <- nodes$start
}
mid <- (nodes$start + nodes$end) / 2
nodes$x <- sin(mid)
nodes$y <- cos(mid)
nodes$r0 <- 1
}
nodes <- combine_layout_nodes(nodes, as_tibble(graph, active = 'nodes'))
nodes$circular <- circular
nodes
}
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