save training/evaluation metric during training. close #511

R-package/NAMESPACE

@@ -91,6 +91,7 @@ export(mx.symbol.sqrt)
 export(mx.symbol.square)
 export(mxnet.export)
 export(outputs)
+export(mx.metric.logger)
 import(Rcpp)
 import(methods)
 importFrom(DiagrammeR,combine_edges)

R-package/R/callback.R

@@ -1,10 +1,24 @@
+#' @export mx.metric.logger
+mx.metric.logger <- setRefClass("mx.metric.logger", fields = list(train = "numeric", eval="numeric"))
+
 #' Log training metric each period
 #' @export
-mx.callback.log.train.metric <- function(period) {
+mx.callback.log.train.metric <- function(period, logger = NULL) {
   function(iteration, nbatch, env) {
     if (nbatch %% period == 0 && !is.null(env$metric)) {
       result <- env$metric$get(env$train.metric)
       cat(paste0("Batch [", nbatch, "] Train-", result$name, "=", result$value, "\n"))
+      if (!is.null(logger)) {
+        if (class(logger) != "mx.metric.logger") {
+          stop("Invalid mx.metric.logger.")
+        }
+        logger$train <- c(logger$train, result$value)
+        if (!is.null(env$eval.metric)) {
+          result <- env$metric$get(env$eval.metric)
+          cat(paste0("Batch [", nbatch, "] Validation-", result$name, "=", result$value, "\n"))
+          logger$eval <- c(logger$eval, result$value)
+        }
+      }
     }
   }
 }