fix issue go-gota#169

dataframe/dataframe.go

@@ -1219,17 +1219,22 @@ func LoadRecords(records [][]string, options ...LoadOption) DataFrame {
 	types := make([]series.Type, len(headers))
 	rawcols := make([][]string, len(headers))
 	for i, colname := range headers {
+		t, useCustomType := cfg.types[colname]
 		rawcol := make([]string, len(records))
 		for j := 0; j < len(records); j++ {
 			rawcol[j] = records[j][i]
+			if useCustomType && t == series.String {
+				// skip the convertion when using custom string type
+				continue
+			}
 			if findInStringSlice(rawcol[j], cfg.nanValues) != -1 {
 				rawcol[j] = "NaN"
 			}
 		}
 		rawcols[i] = rawcol
 
-		t, ok := cfg.types[colname]
-		if !ok {
+		// try to auto detect the data type
+		if !useCustomType {
 			t = cfg.defaultType
 			if cfg.detectTypes {
 				if l, err := findType(rawcol); err == nil {