add collapse_rows html
diff --git a/R/collapse_rows.R b/R/collapse_rows.R
new file mode 100644
index 0000000..57d8987
--- /dev/null
+++ b/R/collapse_rows.R
@@ -0,0 +1,81 @@
+#' Collapse repeat rows to multirow cell
+#'
+#' @export
+collapse_rows <- function(kable_input, columns) {
+  if (is.null(columns)) {
+    stop("Please specify numeric positions of columns you want to collapse.")
+  }
+  kable_format <- attr(kable_input, "format")
+  if (!kable_format %in% c("html", "latex")) {
+    message("Currently generic markdown table using pandoc is not supported.")
+    return(kable_input)
+  }
+  if (kable_format == "html") {
+    return(collapse_rows_html(kable_input, columns))
+  }
+  if (kable_format == "latex") {
+    return(collapse_rows_latex(kable_input, columns))
+  }
+}
+
+collapse_rows_html <- function(kable_input, columns) {
+  kable_attrs <- attributes(kable_input)
+  kable_xml <- read_xml(as.character(kable_input), options = "COMPACT")
+  kable_tbody <- xml_tpart(kable_xml, "tbody")
+
+  kable_dt <- rvest::html_table(xml2::read_html(as.character(kable_input)))[[1]]
+  kable_dt$row_id <- rownames(kable_dt)
+  collapse_matrix <- collapse_row_matrix(kable_dt, columns)
+
+  for (i in 1:nrow(collapse_matrix)) {
+    matrix_row <- collapse_matrix[i, ]
+    if (sum(matrix_row) != length(matrix_row)) {
+      target_row <- xml_child(kable_tbody, i)
+      row_node_rm_count <- 0
+      for (j in 1:length(matrix_row)) {
+        if (matrix_row[j] != 1) {
+          collapsing_col <- as.numeric(sub("x", "", names(matrix_row)[j])) -
+            row_node_rm_count
+          target_cell <- xml_child(target_row, collapsing_col)
+          if (matrix_row[j] == 0) {
+            xml_remove(target_cell)
+            row_node_rm_count <- row_node_rm_count + 1
+          } else {
+            xml_attr(target_cell, "rowspan") <- matrix_row[j]
+            xml_attr(target_cell, "style") <- paste0(
+              xml_attr(target_cell, "style"),
+              "vertical-align: middle !important;")
+          }
+        }
+      }
+    }
+  }
+
+  out <- structure(as.character(kable_xml), format = "html",
+                   class = "knitr_kable")
+  attributes(out) <- kable_attrs
+  return(out)
+}
+
+collapse_rows_latex <- function(kable_input, columns) {
+  # table_info <- magic_mirror(kable_input)
+  # target_row <- table_info$contents[row + 1]
+  # new_row <- latex_row_cells(target_row)
+  # if (bold) {
+  #   new_row <- lapply(new_row, function(x) {
+  #     paste0("\\\\bfseries{", x, "}")
+  #   })
+  # }
+  # if (italic) {
+  #   new_row <- lapply(new_row, function(x) {
+  #     paste0("\\\\em{", x, "}")
+  #   })
+  # }
+  # new_row <- paste(unlist(new_row), collapse = " & ")
+  #
+  # out <- sub(target_row, new_row, as.character(kable_input), perl = T)
+  # out <- structure(out, format = "latex", class = "knitr_kable")
+  # attr(out, "original_kable_meta") <- table_info
+  # return(out)
+  kable_input
+}