Add script to approximate centromere locations

scripts/centromeres.R

@@ -0,0 +1,59 @@
+library(data.table)
+
+# This depends on the current development version of this package to be
+# installed in order to retrieve the distance data.
+distances <- geposan::distances
+
+setorder(distances, "start_position")
+
+chromosomes <- distances[,
+    .(chromosome_length = max(end_position)),
+    by = c("species", "chromosome_name")
+]
+
+handle_chromosome <- function(species_, chromosome_name_) {
+    chromosome_distances <- distances[
+        species == species_ & chromosome_name == chromosome_name_
+    ]
+
+    chromosome_distances[,
+        center_position := mean(c(start_position, end_position)),
+        by = gene
+    ]
+
+    setorder(chromosome_distances, center_position)
+
+    chromosome_distances[1, gap_size := 0]
+
+    for (index in 2:nrow(chromosome_distances)) {
+        previous_end_position <- chromosome_distances[index - 1, end_position]
+        chromosome_distances[
+            index,
+            gap_size := start_position - previous_end_position
+        ]
+    }
+
+    chromosome_gaps <- chromosome_distances[order(gap_size, decreasing = TRUE)]
+
+    # Retrieve the two largest gap sizes.
+    max_gap_size <- chromosome_gaps[1, gap_size]
+    next_gap_size <- chromosome_gaps[2, gap_size]
+
+    list(
+        centromere_start = chromosome_distances[
+            which.max(gap_size) - 1,
+            end_position
+        ],
+        centromere_end = chromosome_distances[
+            which.max(gap_size),
+            start_position
+        ],
+        centromere_dominance = max_gap_size / next_gap_size
+    )
+}
+
+chromosomes[,
+    c("centromere_start", "centromere_end", "centromere_dominance") :=
+        handle_chromosome(species, chromosome_name),
+    by = c("species", "chromosome_name")
+]