diff --git a/R/plot_grid.R b/R/plot_grid.R
index 162afe4..4f86e5c 100644
--- a/R/plot_grid.R
+++ b/R/plot_grid.R
@@ -1,240 +1,241 @@
-#' Arrange multiple plots into a grid
-#'
-#' Arrange multiple plots into a grid.
-#' @param ... List of plots to be arranged into the grid. The plots can be any objects that
-#'   the function [as_gtable()] can handle (see also examples).
-#' @param plotlist (optional) List of plots to display. Alternatively, the plots can be provided
-#' individually as the first n arguments of the function plot_grid (see examples).
-#' @param align (optional) Specifies whether graphs in the grid should be horizontally ("h") or
-#'  vertically ("v") aligned. Options are "none" (default), "hv" (align in both directions), "h", and "v".
-#' @param axis (optional) Specifies whether graphs should be aligned by the left ("l"), right ("r"), top ("t"), or bottom ("b")
-#'  margins. Options are "none" (default), or a string of any combination of l, r, t, and b in any order (e.g. "tblr" or "rlbt" for aligning all margins).
-#'  Must be specified if any of the graphs are complex (e.g. faceted) and alignment is specified and desired. See [align_plots()] for details.
-#' @param greedy (optional) How should margins be adjusted during alignment. See [align_plots()] for details.
-#' @param nrow (optional) Number of rows in the plot grid.
-#' @param ncol (optional) Number of columns in the plot grid.
-#' @param rel_widths (optional) Numerical vector of relative columns widths. For example, in a two-column
-#'              grid, \code{rel_widths = c(2, 1)} would make the first column twice as wide as the
-#'              second column.
-#' @param rel_heights (optional) Numerical vector of relative rows heights. Works just as
-#'              \code{rel_widths} does, but for rows rather than columns.
-#' @param labels (optional) List of labels to be added to the plots. You can also set \code{labels="AUTO"} to
-#'              auto-generate upper-case labels or \code{labels="auto"} to auto-generate lower-case labels.
-#' @param label_size (optional) Numerical value indicating the label size. Default is 14.
-#' @param label_fontfamily (optional) Font family of the plot labels. If not provided, is taken from the current theme.
-#' @param label_fontface (optional) Font face of the plot labels. Default is "bold".
-#' @param label_colour (optional) Color of the plot labels. If not provided, is taken from the current theme.
-#' @param label_x (optional) Single value or vector of x positions for plot labels, relative to each subplot.
-#'   Defaults to 0 for all labels. (Each label is placed all the way to the left of each plot.)
-#' @param label_y (optional) Single value or vector of y positions for plot labels, relative to each subplot.
-#'   Defaults to 1 for all labels. (Each label is placed all the way to the top of each plot.)
-#' @param hjust Adjusts the horizontal position of each label. More negative values move the label further
-#'   to the right on the plot canvas. Can be a single value (applied to all labels) or a vector of values
-#'   (one for each label). Default is -0.5.
-#' @param vjust Adjusts the vertical position of each label. More positive values move the label further
-#'   down on the plot canvas. Can be a single value (applied to all labels) or a vector of values
-#'   (one for each label). Default is 1.5.
-#' @param scale Individual number or vector of numbers greater than 0. Enables you to scale the size of all or
-#'   select plots. Usually it's preferable to set margins instead of using `scale`, but `scale` can
-#'   sometimes be more powerful.
-#' @param byrow Logical value indicating if the plots should be arrange by row (default) or by column.
-#' @param rows Deprecated. Use \code{nrow}.
-#' @param cols Deprecated. Use \code{ncol}.
-#' @examples
-#' library(ggplot2)
-#'
-#' df <- data.frame(
-#'   x = 1:10, y1 = 1:10, y2 = (1:10)^2, y3 = (1:10)^3, y4 = (1:10)^4
-#' )
-#'
-#' p1 <- ggplot(df, aes(x, y1)) + geom_point()
-#' p2 <- ggplot(df, aes(x, y2)) + geom_point()
-#' p3 <- ggplot(df, aes(x, y3)) + geom_point()
-#' p4 <- ggplot(df, aes(x, y4)) + geom_point()
-#' p5 <- ggplot(mpg, aes(as.factor(year), hwy)) +
-#'         geom_boxplot() +
-#'         facet_wrap(~class, scales = "free_y")
-#' # simple grid
-#' plot_grid(p1, p2, p3, p4)
-#'
-#' # simple grid with labels and aligned plots
-#' plot_grid(
-#'   p1, p2, p3, p4,
-#'   labels = c('A', 'B', 'C', 'D'),
-#'   align="hv"
-#' )
-#'
-#' # manually setting the number of rows, auto-generate upper-case labels
-#' plot_grid(p1, p2, p3,
-#'   nrow = 3,
-#'   labels = "AUTO",
-#'   label_size = 12,
-#'   align = "v"
-#' )
-#'
-#' # making rows and columns of different widths/heights
-#' plot_grid(
-#'   p1, p2, p3, p4,
-#'   align = 'hv',
-#'   rel_heights = c(2,1),
-#'   rel_widths = c(1,2)
-#' )
-#'
-#' # aligning complex plots in a grid
-#' plot_grid(
-#'   p1, p5,
-#'   align = "h", axis = "b", nrow = 1, rel_widths = c(1, 2)
-#' )
-#'
-#' # more examples
-#' \donttest{
-#' #' # missing plots in some grid locations, auto-generate lower-case labels
-#' plot_grid(
-#'   p1, NULL, NULL, p2, p3, NULL,
-#'   ncol = 2,
-#'   labels = "auto",
-#'   label_size = 12,
-#'   align = "v"
-#' )
-#'
-#' # can arrange plots on the grid by column as well as by row.
-#' plot_grid(
-#'   p1, NULL, p2, NULL, p3,
-#'   ncol = 2,
-#'   byrow = TRUE
-#' )
-#'
-#' # can align top of plotting area as well as bottom
-#' plot_grid(
-#'   p1, p5,
-#'   align = "h", axis = "tb",
-#'   nrow = 1, rel_widths = c(1, 2)
-#' )
-#'
-#' # other types of plots not generated with ggplot
-#' p6 <- ~{
-#'   par(
-#'     mar = c(3, 3, 1, 1),
-#'     mgp = c(2, 1, 0)
-#'   )
-#'   plot(sqrt)
-#' }
-#'
-#' p7 <- function() {
-#'   par(
-#'     mar = c(2, 2, 1, 1),
-#'     mgp = c(2, 1, 0)
-#'   )
-#'   image(volcano)
-#' }
-#' p8 <- grid::circleGrob()
-#'
-#' plot_grid(p1, p6, p7, p8, labels = "AUTO", scale = c(1, .9, .9, .7))
-#' }
-#' @export
-plot_grid <- function(..., plotlist = NULL, align = c("none", "h", "v", "hv"),
-                      axis = c("none", "l", "r", "t", "b", "lr", "tb", "tblr"),
-                      nrow = NULL, ncol = NULL, rel_widths = 1,
-                      rel_heights = 1, labels = NULL, label_size = 14,
-                      label_fontfamily = NULL, label_fontface = "bold", label_colour = NULL,
-                      label_x = 0, label_y = 1,
-                      hjust = -0.5, vjust = 1.5, scale = 1., greedy = TRUE,
-                      byrow = TRUE, cols = NULL, rows = NULL) {
-
-  # Make a list from the ... arguments and plotlist
-  plots <- c(list(...), plotlist)
-  num_plots <- length(plots)
-
-  if (!is.null(cols)){
-    warning("Argument 'cols' is deprecated. Use 'ncol' instead.")
-  }
-
-  if (!is.null(rows)){
-    warning("Argument 'rows' is deprecated. Use 'nrow' instead.")
-  }
-
-  scale <- rep_len(scale, num_plots)
-  if (sum(scale <= 0) > 1){
-    stop("Argument 'scale' needs to be greater than 0.")
-  }
-
-  # internally, this function operates with variables cols and rows instead of ncol and nrow
-  if (!is.null(ncol)){
-    cols <- ncol
-  }
-  if (!is.null(nrow)){
-    rows <- nrow
-  }
-
-
-  # calculate grid dimensions
-  if (is.null(cols) && is.null(rows)){
-    # if neither rows nor cols are given, we make a square grid
-    cols <- ceiling(sqrt(num_plots))
-    rows <- ceiling(num_plots/cols)
-  }
-  # alternatively, we know at least how many rows or how many columns we need
-  if (is.null(cols)) cols <- ceiling(num_plots/rows)
-  if (is.null(rows)) rows <- ceiling(num_plots/cols)
-
-  # if the user wants to layout the plots by column, we use the calculated rows to reorder plots and labels
-  if (!isTRUE(byrow)) 
-    plots <- plots[c(t(matrix(c(1:num_plots, rep(NA, (rows * cols) - num_plots)), nrow = rows, byrow = FALSE)))]
-    labels <- labels[c(t(matrix(c(1:num_plots, rep(NA, (rows * cols) - num_plots)), nrow = rows, byrow = FALSE)))]
-
-  # Align the plots (if specified)
-  grobs <- align_plots(plotlist = plots, align = align, axis = axis, greedy = greedy)
-
-  if ("AUTO" %in% labels)
-    labels <- LETTERS[1:num_plots]
-  else if ("auto" %in% labels)
-    labels <- letters[1:num_plots]
-
-  # label adjustments can be provided globally for all labels
-  # or individually for each label
-  hjust <- rep_len(hjust, length(labels))
-  vjust <- rep_len(vjust, length(labels))
-  label_x <- rep_len(label_x, length(labels))
-  label_y <- rep_len(label_y, length(labels))
-
-  # calculate appropriate vectors of rel. heights and widths
-  rel_heights <- rep(rel_heights, length.out = rows)
-  rel_widths <- rep(rel_widths, length.out = cols)
-  # calculate the appropriate coordinates and deltas for each row and column
-  x_deltas <- rel_widths/sum(rel_widths)
-  y_deltas <- rel_heights/sum(rel_heights)
-  xs <- cumsum(rel_widths)/sum(rel_widths) - x_deltas
-  ys <- 1 - cumsum(rel_heights)/sum(rel_heights)
-
-  # now place all the plots
-  p <- ggdraw() # start with nothing
-  col_count <- 0
-  row_count <- 1
-  for (i in 1:(rows*cols)){
-    if (i > num_plots) break
-
-    x_delta <- x_deltas[col_count+1]
-    y_delta <- y_deltas[row_count]
-    x <- xs[col_count+1]
-    y <- ys[row_count]
-
-    # place the plot
-    p_next <- grobs[[i]]
-    if (!is.null(p_next)){
-      p <- p + draw_grob(p_next, x, y, x_delta, y_delta, scale[i])
-    }
-    # place a label if we have one
-    if (i <= length(labels)){
-      p <- p + draw_plot_label(labels[i], x + label_x[i]*x_delta, y + label_y[i]*y_delta, size = label_size,
-                               family = label_fontfamily, fontface = label_fontface, colour = label_colour,
-                               hjust = hjust[i], vjust = vjust[i])
-    }
-    # move on to next grid position
-    col_count <- col_count + 1
-    if (col_count >= cols){
-      col_count <- 0
-      row_count <- row_count + 1
-    }
-  }
-  p
-}
+#' Arrange multiple plots into a grid
+#'
+#' Arrange multiple plots into a grid.
+#' @param ... List of plots to be arranged into the grid. The plots can be any objects that
+#'   the function [as_gtable()] can handle (see also examples).
+#' @param plotlist (optional) List of plots to display. Alternatively, the plots can be provided
+#' individually as the first n arguments of the function plot_grid (see examples).
+#' @param align (optional) Specifies whether graphs in the grid should be horizontally ("h") or
+#'  vertically ("v") aligned. Options are "none" (default), "hv" (align in both directions), "h", and "v".
+#' @param axis (optional) Specifies whether graphs should be aligned by the left ("l"), right ("r"), top ("t"), or bottom ("b")
+#'  margins. Options are "none" (default), or a string of any combination of l, r, t, and b in any order (e.g. "tblr" or "rlbt" for aligning all margins).
+#'  Must be specified if any of the graphs are complex (e.g. faceted) and alignment is specified and desired. See [align_plots()] for details.
+#' @param greedy (optional) How should margins be adjusted during alignment. See [align_plots()] for details.
+#' @param nrow (optional) Number of rows in the plot grid.
+#' @param ncol (optional) Number of columns in the plot grid.
+#' @param rel_widths (optional) Numerical vector of relative columns widths. For example, in a two-column
+#'              grid, \code{rel_widths = c(2, 1)} would make the first column twice as wide as the
+#'              second column.
+#' @param rel_heights (optional) Numerical vector of relative rows heights. Works just as
+#'              \code{rel_widths} does, but for rows rather than columns.
+#' @param labels (optional) List of labels to be added to the plots. You can also set \code{labels="AUTO"} to
+#'              auto-generate upper-case labels or \code{labels="auto"} to auto-generate lower-case labels.
+#' @param label_size (optional) Numerical value indicating the label size. Default is 14.
+#' @param label_fontfamily (optional) Font family of the plot labels. If not provided, is taken from the current theme.
+#' @param label_fontface (optional) Font face of the plot labels. Default is "bold".
+#' @param label_colour (optional) Color of the plot labels. If not provided, is taken from the current theme.
+#' @param label_x (optional) Single value or vector of x positions for plot labels, relative to each subplot.
+#'   Defaults to 0 for all labels. (Each label is placed all the way to the left of each plot.)
+#' @param label_y (optional) Single value or vector of y positions for plot labels, relative to each subplot.
+#'   Defaults to 1 for all labels. (Each label is placed all the way to the top of each plot.)
+#' @param hjust Adjusts the horizontal position of each label. More negative values move the label further
+#'   to the right on the plot canvas. Can be a single value (applied to all labels) or a vector of values
+#'   (one for each label). Default is -0.5.
+#' @param vjust Adjusts the vertical position of each label. More positive values move the label further
+#'   down on the plot canvas. Can be a single value (applied to all labels) or a vector of values
+#'   (one for each label). Default is 1.5.
+#' @param scale Individual number or vector of numbers greater than 0. Enables you to scale the size of all or
+#'   select plots. Usually it's preferable to set margins instead of using `scale`, but `scale` can
+#'   sometimes be more powerful.
+#' @param byrow Logical value indicating if the plots should be arrange by row (default) or by column.
+#' @param rows Deprecated. Use \code{nrow}.
+#' @param cols Deprecated. Use \code{ncol}.
+#' @examples
+#' library(ggplot2)
+#'
+#' df <- data.frame(
+#'   x = 1:10, y1 = 1:10, y2 = (1:10)^2, y3 = (1:10)^3, y4 = (1:10)^4
+#' )
+#'
+#' p1 <- ggplot(df, aes(x, y1)) + geom_point()
+#' p2 <- ggplot(df, aes(x, y2)) + geom_point()
+#' p3 <- ggplot(df, aes(x, y3)) + geom_point()
+#' p4 <- ggplot(df, aes(x, y4)) + geom_point()
+#' p5 <- ggplot(mpg, aes(as.factor(year), hwy)) +
+#'         geom_boxplot() +
+#'         facet_wrap(~class, scales = "free_y")
+#' # simple grid
+#' plot_grid(p1, p2, p3, p4)
+#'
+#' # simple grid with labels and aligned plots
+#' plot_grid(
+#'   p1, p2, p3, p4,
+#'   labels = c('A', 'B', 'C', 'D'),
+#'   align="hv"
+#' )
+#'
+#' # manually setting the number of rows, auto-generate upper-case labels
+#' plot_grid(p1, p2, p3,
+#'   nrow = 3,
+#'   labels = "AUTO",
+#'   label_size = 12,
+#'   align = "v"
+#' )
+#'
+#' # making rows and columns of different widths/heights
+#' plot_grid(
+#'   p1, p2, p3, p4,
+#'   align = 'hv',
+#'   rel_heights = c(2,1),
+#'   rel_widths = c(1,2)
+#' )
+#'
+#' # aligning complex plots in a grid
+#' plot_grid(
+#'   p1, p5,
+#'   align = "h", axis = "b", nrow = 1, rel_widths = c(1, 2)
+#' )
+#'
+#' # more examples
+#' \donttest{
+#' #' # missing plots in some grid locations, auto-generate lower-case labels
+#' plot_grid(
+#'   p1, NULL, NULL, p2, p3, NULL,
+#'   ncol = 2,
+#'   labels = "auto",
+#'   label_size = 12,
+#'   align = "v"
+#' )
+#'
+#' # can arrange plots on the grid by column as well as by row.
+#' plot_grid(
+#'   p1, NULL, p2, NULL, p3,
+#'   ncol = 2,
+#'   byrow = TRUE
+#' )
+#'
+#' # can align top of plotting area as well as bottom
+#' plot_grid(
+#'   p1, p5,
+#'   align = "h", axis = "tb",
+#'   nrow = 1, rel_widths = c(1, 2)
+#' )
+#'
+#' # other types of plots not generated with ggplot
+#' p6 <- ~{
+#'   par(
+#'     mar = c(3, 3, 1, 1),
+#'     mgp = c(2, 1, 0)
+#'   )
+#'   plot(sqrt)
+#' }
+#'
+#' p7 <- function() {
+#'   par(
+#'     mar = c(2, 2, 1, 1),
+#'     mgp = c(2, 1, 0)
+#'   )
+#'   image(volcano)
+#' }
+#' p8 <- grid::circleGrob()
+#'
+#' plot_grid(p1, p6, p7, p8, labels = "AUTO", scale = c(1, .9, .9, .7))
+#' }
+#' @export
+plot_grid <- function(..., plotlist = NULL, align = c("none", "h", "v", "hv"),
+                      axis = c("none", "l", "r", "t", "b", "lr", "tb", "tblr"),
+                      nrow = NULL, ncol = NULL, rel_widths = 1,
+                      rel_heights = 1, labels = NULL, label_size = 14,
+                      label_fontfamily = NULL, label_fontface = "bold", label_colour = NULL,
+                      label_x = 0, label_y = 1,
+                      hjust = -0.5, vjust = 1.5, scale = 1., greedy = TRUE,
+                      byrow = TRUE, cols = NULL, rows = NULL) {
+
+  # Make a list from the ... arguments and plotlist
+  plots <- c(list(...), plotlist)
+  num_plots <- length(plots)
+
+  if (!is.null(cols)){
+    warning("Argument 'cols' is deprecated. Use 'ncol' instead.")
+  }
+
+  if (!is.null(rows)){
+    warning("Argument 'rows' is deprecated. Use 'nrow' instead.")
+  }
+
+  scale <- rep_len(scale, num_plots)
+  if (sum(scale <= 0) > 1){
+    stop("Argument 'scale' needs to be greater than 0.")
+  }
+
+  # internally, this function operates with variables cols and rows instead of ncol and nrow
+  if (!is.null(ncol)){
+    cols <- ncol
+  }
+  if (!is.null(nrow)){
+    rows <- nrow
+  }
+
+
+  # calculate grid dimensions
+  if (is.null(cols) && is.null(rows)){
+    # if neither rows nor cols are given, we make a square grid
+    cols <- ceiling(sqrt(num_plots))
+    rows <- ceiling(num_plots/cols)
+  }
+  # alternatively, we know at least how many rows or how many columns we need
+  if (is.null(cols)) cols <- ceiling(num_plots/rows)
+  if (is.null(rows)) rows <- ceiling(num_plots/cols)
+
+  # if the user wants to layout the plots by column, we use the calculated rows to reorder plots and labels
+  if (!isTRUE(byrow)){
+    plots <- plots[c(t(matrix(c(1:num_plots, rep(NA, (rows * cols) - num_plots)), nrow = rows, byrow = FALSE)))]
+    labels <- labels[c(t(matrix(c(1:num_plots, rep(NA, (rows * cols) - num_plots)), nrow = rows, byrow = FALSE)))]
+  }
+
+  # Align the plots (if specified)
+  grobs <- align_plots(plotlist = plots, align = align, axis = axis, greedy = greedy)
+
+  if ("AUTO" %in% labels)
+    labels <- LETTERS[1:num_plots]
+  else if ("auto" %in% labels)
+    labels <- letters[1:num_plots]
+
+  # label adjustments can be provided globally for all labels
+  # or individually for each label
+  hjust <- rep_len(hjust, length(labels))
+  vjust <- rep_len(vjust, length(labels))
+  label_x <- rep_len(label_x, length(labels))
+  label_y <- rep_len(label_y, length(labels))
+
+  # calculate appropriate vectors of rel. heights and widths
+  rel_heights <- rep(rel_heights, length.out = rows)
+  rel_widths <- rep(rel_widths, length.out = cols)
+  # calculate the appropriate coordinates and deltas for each row and column
+  x_deltas <- rel_widths/sum(rel_widths)
+  y_deltas <- rel_heights/sum(rel_heights)
+  xs <- cumsum(rel_widths)/sum(rel_widths) - x_deltas
+  ys <- 1 - cumsum(rel_heights)/sum(rel_heights)
+
+  # now place all the plots
+  p <- ggdraw() # start with nothing
+  col_count <- 0
+  row_count <- 1
+  for (i in 1:(rows*cols)){
+    if (i > num_plots) break
+
+    x_delta <- x_deltas[col_count+1]
+    y_delta <- y_deltas[row_count]
+    x <- xs[col_count+1]
+    y <- ys[row_count]
+
+    # place the plot
+    p_next <- grobs[[i]]
+    if (!is.null(p_next)){
+      p <- p + draw_grob(p_next, x, y, x_delta, y_delta, scale[i])
+    }
+    # place a label if we have one
+    if (i <= length(labels)){
+      p <- p + draw_plot_label(labels[i], x + label_x[i]*x_delta, y + label_y[i]*y_delta, size = label_size,
+                               family = label_fontfamily, fontface = label_fontface, colour = label_colour,
+                               hjust = hjust[i], vjust = vjust[i])
+    }
+    # move on to next grid position
+    col_count <- col_count + 1
+    if (col_count >= cols){
+      col_count <- 0
+      row_count <- row_count + 1
+    }
+  }
+  p
+}