start of goodness of fit function - a lot of going around in circles...

R/normalitycheck.R

@@ -0,0 +1,50 @@
+data <- data.frame(x = rnorm(n = 1500, mean = 20, sd = 1)^(-3))
+
+histplot <- ggplot2::ggplot(data, ggplot2::aes(x = x)) + 
+  ggplot2::geom_histogram(bins = ifelse(nrow(data) < 31, 7, 11), 
+                          fill = "aquamarine3", colour = "black") +
+  ggplot2::theme_bw() + 
+  ggplot2::labs(y = "Frequency", x = "")
+histplot  
+
+stest <- shapiro.test(data$x)
+
+
+power_val <- c(-5, -4, -3, -2, -1, -0.5, 0.5, 2, 3, 4, 5)  
+
+trans_tab <- data.frame(Transformation = c(paste("y^", power_val, sep = ""), "ln(y)"),
+pval = NA)
+
+# Trying standard transformations
+for(i in 1:length(power_val)){
+  newdat <- data$x^(power_val[i])
+  trans_tab$pval[i] <- round(shapiro.test(newdat)$p.value,3)
+}
+newdat <- log(data$x)
+trans_tab$pval[trans_tab$Transformation == "ln(y)"] <- round(shapiro.test(newdat)$p.value,3)
+trans_tab
+
+trans <- trans_tab$Transformation[which.max(ifelse(trans_tab$pval > 0.05, trans_tab$pval, NA))]
+
+numb_obs <- paste0("Number of observations: ", length(!is.na(data$x)), " \n")
+
+
+shapiro_text <- paste0("Shapiro-Wilk's test p-value = ", round(stest$p.value,3), ". \n")
+
+shapiro_interp <-
+if(stest$p.value > 0.05){"Shapiro-Wilk's test indicates the distribution \n is similar to the normal distribution. \n Transformation not required." } else{
+paste0("Shapiro-Wilk's test indicates the distribution \n deviates from the normal distribution. \n", 
+       "Try a transformation based on ", 
+                     trans, ". \n")
+}
+
+res_text <- paste0(numb_obs, shapiro_text, shapiro_interp)
+
+res_text_graph <- ggplot2::ggplot() + 
+  ggplot2::annotate("text", x = 4, y = 25, size = 6, label = res_text) + 
+  ggplot2::theme_void()
+
+library(cowplot)
+plot_grid(histplot, res_text_graph, ncol = 1)
+
+