added solutions to session 2

DataWork/Code/1-intro-to-R-solutions.R

@@ -1,6 +1,7 @@
 ## R for Stata Users
 ## March 2023
 ## Exercise solutions 
+## Session: Introduction to R
 
 ## Exercise 1 ====
 whr <- read.csv("/path/to/data/file")

DataWork/Code/2-intro-to-R-programming-solutions.R

@@ -0,0 +1,53 @@
+## R for Stata Users
+## March 2023
+## Exercise solutions 
+## Session: Introduction to R programming
+
+## Exercise 1 ====
+# (no coding needed for exercise)
+
+## Exercise 2 ====
+# (no coding needed for exercise)
+
+## Exercise 3 ====
+library(here)
+whr <- read.csv(here("DataWork", "DataSets", "Final", "whr_panel.csv"))
+# note that this will only work if exercise 2
+# was executed correctly
+
+## Exercise 4 ====
+#install.packages("dplyr") # uncomment installation if needed
+#install.packages("purrr") # uncomment installation if needed
+library(dply)
+library(purrr)
+
+## Exercise 5 ====
+# Create dataframe
+df <- data.frame(replicate(50000, sample(1:100, 400, replace=TRUE)))
+# Create empty vector
+col_means_loop <- c()
+# Loop and append means to vector (will take a few seconds)
+for (column in df){
+  col_means_loop <- append(col_means_loop, mean(column))
+}
+
+## Exercise 6 ====
+col_means_map <- map(df, mean)
+# this will only work if you defined df in exercise 5
+
+## Exercise 7 ====
+zscore <- function(x) {
+  mean <- mean(x, na.rm = TRUE)
+  sd   <- sd(x, na.rm = TRUE)
+  z    <- (x - mean)/sd
+  return(z)
+}
+
+## Exercise 8 ====
+z_scores <- whr %>%
+  select(health_life_expectancy, freedom) %>%
+  map(zscore)
+whr$hle_st <- z_scores[[1]]
+whr$freedom_st <- z_scores[[2]]
+# this will only run if you created the function
+# zscores() in exercise 7