Help fixing #1540 (#1638)

* Help fixing #1540

* Handle character matrix corner case

* Update with recommendation in #1638

R-package/R/lgb.Predictor.R

@@ -79,8 +79,8 @@ Predictor <- R6::R6Class(
       # Set temporary variable
       num_row <- 0L
 
-      # Check if data is a file name
-      if (is.character(data)) {
+      # Check if data is a file name and not a matrix
+      if (identical(class(data), "character") && length(data) == 1) {
 
         # Data is a filename, create a temporary file with a "lightgbm_" pattern in it
         tmp_filename <- tempfile(pattern = "lightgbm_")
@@ -97,7 +97,7 @@ Predictor <- R6::R6Class(
           lgb.c_str(tmp_filename))
 
         # Get predictions from file
-        preds <- read.delim(tmp_filename, header = FALSE, seq = "\t")
+        preds <- read.delim(tmp_filename, header = FALSE, sep = "\t")
         num_row <- nrow(preds)
         preds <- as.vector(t(preds))