Add basic histograms

This adds some basic histograms to show the distribution of age at
transplatation and year of transplatation.

plots.R

@@ -5,8 +5,10 @@
 
 source("survival.R")
 source("secmal.R")
+source("visualize.R")
 
 #
 # Make all plots and save to file
 sma_plot_file_surv()
 sma_plot_file_secmal()
+sma_plot_file_hist()

visualize.R

@@ -0,0 +1,22 @@
+# Visualize basics from data
+#
+# License: GPL version 3
+# Jens Mathis Sauer (c) 2020
+
+source("utils.R")
+sma_init()
+
+sma_hist_asct_age <- function() {
+	data <- data.frame(asct_age = secmal$asct_age)
+	ggplot(data, aes(x = asct_age)) + geom_histogram(binwidth = 5)
+}
+
+sma_hist_asct_year <- function() {
+	data <- data.frame(asct_year = secmal$asct_year)
+	ggplot(data, aes(x = asct_year)) + geom_histogram(binwidth = 1)
+}
+
+sma_plot_file_hist <- function() {
+	sma_plot_file("hist_asct_age.png", png, sma_hist_asct_age)
+	sma_plot_file("hist_asct_year.png", png, sma_hist_asct_year)
+}