introduce customisable month_label_string for support to other langua…

…ges and other use cases, fixes #46

DESCRIPTION

@@ -11,7 +11,7 @@ Description: 'ganttrify' facilitates the creation of nice-looking Gantt charts,
 License: GPL-3
 Encoding: UTF-8
 LazyData: true
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.0
 Imports: 
     magrittr,
     tibble,

R/ganttrify.R

@@ -17,6 +17,7 @@
 #' @param size_text_relative Numeric, defaults to 1. Changes the size of all textual elements relative to their default size. If you set this to e.g. 1.5 all text elements will be 50\% bigger.
 #' @param label_wrap Defaults to FALSE. If given, must be numeric, referring to the number of characters per line allowed in the labels of projects and activities, or logical (if set to TRUE, it will default to 32). To be used when labels would otherwise be excessively long.
 #' @param month_number_label Logical, defaults to TRUE. If TRUE, it includes month numbering on x axis.
+#' @param month_label_string Defaults to "M", relevant only if `month_number_label` is set to \code{TRUE}. String that precedes the month number: e.g. if set to "M", then months are labeled as "M1", "M2", etc. 
 #' @param month_date_label Logical, defaults to TRUE. If TRUE, it includes month names and dates on the x axis.
 #' @param x_axis_position Logical, defaults to "top". Can also be "bottom". Used only when only one of `month_number_label` and `month_date_label` is TRUE, otherwise ignored.
 #' @param colour_stripe Character, defaults to "lightgray". This is the stripe colour in the background used in alternate months.
@@ -58,6 +59,7 @@ ganttrify <- function(project,
                       size_text_relative = 1,
                       label_wrap = FALSE,
                       month_number_label = TRUE,
+                      month_label_string = "M",
                       month_date_label = TRUE,
                       x_axis_position = "top",
                       colour_stripe = "lightgray",
@@ -253,7 +255,7 @@ ganttrify <- function(project,
                             breaks = date_breaks,
                             date_labels = "%b\n%Y",
                             minor_breaks = NULL,
-                            sec.axis = ggplot2::dup_axis(labels = paste0("M", seq_along(date_breaks)*month_breaks-(month_breaks-1))))
+                            sec.axis = ggplot2::dup_axis(labels = paste0(month_label_string, seq_along(date_breaks)*month_breaks-(month_breaks-1))))
 
 
   } else if (month_number_label==FALSE&month_date_label==TRUE) {
@@ -267,7 +269,7 @@ ganttrify <- function(project,
     gg_gantt <- gg_gantt +
       ggplot2::scale_x_date(name = "",
                             breaks = date_breaks,
-                            date_labels = paste0("M", seq_along(date_breaks)),
+                            date_labels = paste0(month_label_string, seq_along(date_breaks)),
                             minor_breaks = NULL,
                             position = x_axis_position)
   } else if (month_number_label==FALSE&month_date_label==FALSE) {