Handle caching

R/utils.R

@@ -1,3 +1,34 @@
+# Cache the value of an expression on the file system.
+#
+# The expression will be evaluated if there is no matching cache file found.
+# The cache files will be located in a directory "cache" located in the current
+# working directory.
+#
+# @param name Human readable part of the cache file name.
+# @param objects A vector of objects that this expression depends on. The hash
+#   of those objects will be used for identifying the cache file.
+cached <- function(name, objects, expr) {
+    if (!dir.exists("cache")) {
+        dir.create("cache")
+    }
+
+    id <- rlang::hash(objects)
+    cache_file <- sprintf("cache/%s_%s.rda", name, id)
+
+    if (file.exists(cache_file)) {
+        # If the cache file exists, we restore the data from it.
+        load(cache_file)
+    } else {
+        # If the cache file doesn't exist, we have to do the computation.
+        data <- expr
+
+        # The results are cached for the next run.
+        save(data, file = cache_file, compress = "xz")
+    }
+
+    data
+}
+
 # This is needed to make data.table's symbols available within the package.
 #' @import data.table
 NULL