R - Function

• Function in R
• is a R Object of class "function"
• It has "named arguments" with default values, i.e. mean function in R calculates the arithmetic mean, it has na.rm arguments with default value "FALSE".

 > x <- c(1,2,NA,5)  
 > mean(x)  # can't calculate mean because of the NA value
 [1] NA  
 > mean(x,na.rm = TRUE)  # turn on remove NA value argument
 [1] 2.666667  
 > mean(na.rm = TRUE, x) # the same even change the position of arguments
 [1] 2.666667  

• Define a sum function to return sum of two arguments

 > sumfun <- function(x,y){  
 +   return(x+y)  
 + }  
 > sumfun(1,4)  
 [1] 5  

• Lazy Evaluation: evaluated only while needed

 > f <- function(x,y){  
 +   x*2  # no evaluation for y, the same as return(x*2)
 + }  
 > f(4)  # return result without error
 [1] 8  

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