Data commit

Task/Truncate-a-file/R/truncate-a-file.r

@@ -0,0 +1,28 @@
+truncate_file <- function(filename, n_bytes) {
+
+  # check file exists and size is greater than n_bytes
+  stopifnot(
+    "file does not exist"= file.exists(filename),
+    "not enough bytes in file"= file.size(filename) >= n_bytes
+  )
+
+  # read bytes from input file
+  input.con <- file(filename, "rb")
+  bindata <- readBin(input.con, integer(), n=n_bytes/4)
+  close(input.con)
+
+  # write bytes to temporary file
+  tmp.filename <- tempfile()
+  output.con <- file(tmp.filename, "wb")
+  writeBin(bindata, output.con)
+  close(output.con)
+
+  # double check that everything worked before overwriting original file
+  stopifnot(
+    "temp file is not expected size"= file.size(tmp.filename) == n_bytes
+  )
+
+  # overwrite input file with temporary file
+  file.rename(tmp.filename, filename)
+
+}