diff --git a/R/cross.R b/R/cross.R
index 5aacb19..988e791 100644
--- a/R/cross.R
+++ b/R/cross.R
@@ -714,7 +714,7 @@ margin_from_cases = function(cases, margin = c("columns", "rows", "total")){
                     rows =  "cell_var",
                     total =  NULL
     )
-    by_str = paste(c(row_var_name, margin), collapse = ",")    
+    by_str = c(row_var_name, margin)
     dtotal = cases[, list(total = sum(value, na.rm = TRUE)), by = by_str]
     dtotal
 }
@@ -792,7 +792,7 @@ calculate_response_column_margin = function(raw_data,
     value = NULL
     if(stat_type=="cpct_responses" || any(total_statistic %in% c("u_responses", "w_responses"))){  
         if(has_row_var(raw_data)){
-            by_str = "row_var,col_var"
+            by_str = c("row_var", "col_var")
         } else {
             by_str = "col_var"
         }
@@ -875,7 +875,7 @@ rbindlist_and_aggregate = function(list_of_datatables){
        list_of_datatables = unlist(list_of_datatables, recursive = FALSE, use.names = FALSE)    
     }
     res = rbindlist(list_of_datatables, use.names = FALSE, fill = FALSE)
-    by_str = paste(colnames(res)[!(colnames(res) %in% "value")], collapse = ",")
+    by_str = setdiff(colnames(res), "value")
     res[, list(value = sum(value, na.rm = TRUE)), by = by_str]
      
 }
@@ -897,7 +897,7 @@ internal_cases = function(raw_data, col_var_names, cell_var_names = NULL, use_we
     if(is.null(col_var_names)) col_var_names = list(NULL) 
     res = lapply(cell_var_names, function(each_cell) { 
         res = lapply(col_var_names, function(each_col){
-            by_str = paste(c(row_var_name, each_cell, each_col), collapse = ",")
+            by_str = c(row_var_name, each_cell, each_col)
             if(use_weight){
                 dres = raw_data[, list(value = sum(weight, na.rm = TRUE)), 
                                 by = by_str] 
diff --git a/R/cross_fun.R b/R/cross_fun.R
index a1cf23a..98aea55 100644
--- a/R/cross_fun.R
+++ b/R/cross_fun.R
@@ -500,7 +500,7 @@ elementary_cro_fun_df = function(cell_var,
 
     
     # statistics
-    by_string = "..row_var__,..col_var__"
+    by_string = c("..row_var__", "..col_var__")
     if(is.logical(use_lapply) && !use_lapply){
         if(is.null(weight)){
             dtable = raw_data[ , fun(.SD), by = by_string]
diff --git a/R/window_fun.R b/R/window_fun.R
index 18e8a6b..59117ec 100644
--- a/R/window_fun.R
+++ b/R/window_fun.R
@@ -36,8 +36,7 @@ window_fun.default = function(x, ...){
                "`window_fun` - all variables should be of the same length or length 1.")
         dt_table = as.data.table(c(list(x), grouping_variables))
         setnames(dt_table, c("x", grouping_names))
-        by_string = paste(grouping_names, collapse = ",")
-        dt_table[, res:=eval(expr), by = by_string]
+        dt_table[, res:=eval(expr), by = grouping_names]
         dt_table[["res"]]
     } else {
         rep(fun(x), length(x))