feat: New ns_graph() and lower-level ns_df() and ns_metadata() to download from [netzschleuder](https://networks.skewed.de)

NAMESPACE

@@ -1,6 +1,8 @@
 # Generated by roxygen2: do not edit by hand
 
+export(graph_from_netzschleuder)
 export(lesmis_gml)
 export(lesmis_graphml)
 export(lesmis_pajek)
+export(read_from_netzschleuder)
 importFrom(igraph,vcount)

R/netzschleuder.R

@@ -0,0 +1,80 @@
+#' Download a graph from the Netzschleuder data catalogue
+#' Netzschleuder (<https://networks.skewed.de/>) is a large online repository for
+#' network datasets with the aim of aiding scientific research.
+#' @param name character. name of the network dataset.
+#' @param net character. If the dataset contains several networks this is the network name.
+#' @return a named list containing an edge list and node attribute data frame and some metadata
+#' @export
+read_from_netzschleuder <- function(name, net = NULL) {
+  if (is.null(net)) {
+    net <- name
+  }
+  zip_url <- paste0(
+    "https://networks.skewed.de/net/",
+    name,
+    "/files/",
+    net,
+    ".csv.zip"
+  )
+
+  temp <- tempfile()
+  utils::download.file(zip_url, temp, quiet = TRUE) #TODO: add better error handling
+  zip_contents <- utils::unzip(temp, list = TRUE)
+
+  edge_file_name <- zip_contents$Name[grepl("edge", zip_contents$Name)]
+  node_file_name <- zip_contents$Name[grepl("node", zip_contents$Name)]
+  meta_file_name <- zip_contents$Name[grepl("gprops", zip_contents$Name)]
+
+  edges_df <- utils::read.csv(unz(temp, edge_file_name)) + 1
+  names(edges_df)[c(1, 2)] <- c("from", "to")
+
+  nodes_df <- utils::read.csv(unz(temp, node_file_name))
+  names(nodes_df)[1] <- "id"
+  nodes_df$id <- nodes_df$id + 1
+  if ("X_pos" %in% names(nodes_df)) {
+    pos_array <- gsub("array\\(\\[|\\]|\\)", "", nodes_df[["X_pos"]])
+    split_coords <- strsplit(pos_array, ",")
+
+    x_vals <- sapply(split_coords, function(x) as.numeric(trimws(x[1])))
+    y_vals <- sapply(split_coords, function(x) as.numeric(trimws(x[2])))
+
+    nodes_df[["X_pos"]] <- NULL
+    nodes_df$x <- x_vals
+    nodes_df$y <- y_vals
+  }
+
+  meta_df <- utils::read.csv(unz(temp, meta_file_name))
+  on.exit(unlink(temp))
+
+  list(nodes = nodes_df, edges = edges_df, meta = meta_df)
+}
+
+#' Create a graph from the Netzschleuder data catalogue
+#'
+#' Netzschleuder (<https://networks.skewed.de/>) is a large online repository for
+#' network datasets with the aim of aiding scientific research.
+#' @param name character. name of the network dataset.
+#' @param net character. If the dataset contains several networks this is the network name.
+#' @param directed logical. Whether a directed graph is constructed.
+#' @param bipartite logical. Whether a bipartite graph is constructed.
+#' @return a new graph object.
+#' @export
+graph_from_netzschleuder <- function(
+  name,
+  net = NULL,
+  directed = FALSE,
+  bipartite = FALSE
+) {
+  graph_data <- read_from_netzschleuder(name, net)
+  g <- igraph::graph_from_data_frame(
+    graph_data$edges,
+    directed = directed,
+    vertices = graph_data$nodes
+  )
+  if (bipartite) {
+    types <- rep(FALSE, igraph::vcount(g))
+    types[graph_data$nodes$id %in% graph_data$edges[, 1]] <- TRUE
+    g <- igraph::set_vertex_attr(g, "type", value = types)
+  }
+  g
+}