Merge pull request #23 from ScHARR-PHEDS/custom_functions

session 6 on new branch

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scripts/session_6.R

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+#=============
+# R4ScHARR 
+# Robert Smith, Paul Schneider & Sarah Bates
+# Session 6 Script
+#============= 
+
+
+#====================#
+#  For loops ----
+#====================#
+
+# For loops can be used to repeat the same action multiple times without lots of 
+# lines of code. This is a simple function to print list of numbers
+for(i in 1:10) {                                           
+
+  print(i)                                               
+}
+
+# It's useful to when applying a function to all rows or columns of a dataset
+
+# recreate simple data frame used previously
+
+height <- c(1.38,1.45,1.21,1.56) # combine is used to create the vector.
+weight <- c(45,42,43,50)
+first_name <- c("Alice","Bob","Harry","Jane")
+sex <- factor(x = c("F","M","M","F"))
+df <- data.frame(height,weight,first_name,sex)
+df$bmi <- df$weight / df$height^2 
+
+# use the for loop to report each persons height
+for (i in 1:nrow(df)) {
+
+  # print combination of the value in column 3 (first name) with the value in column 1 (height)
+  print(paste0(df[i,3], " is ",df[i,1], "m tall"))
+
+}
+
+# use the for loop to change the variable name (column)
+
+for(i in 1:ncol(df)) {          
+
+  # change the name of each column to var followed by the column number
+  colnames(df)[i] <- paste0("Var_", i)              
+}
+
+
+
+
+
+
+
+#====================#
+# 4.2 Custom functions ----
+#====================#
+
+# Creating a custom function can be really useful - reduces lines of code and makes work
+# easily reproducible, clearer and more organised
+
+# The structure of a function is:
+
+#  function_name <- function(arg1, arg2, ... ){
+#   statements
+#    return(object)
+# }
+
+# Here's a simple example 
+
+f_simple <- function(x,y,z){
+
+  value = x + y - z
+
+  return(value)
+
+}
+
+# to see the details of the function you can just run the name
+f_simple
+
+# to run the function, add the argument in brackets
+
+f_simple(1,2,3)
+f_simple(6,5,12)
+
+