“Print hello”​ is not enough. A collection of Hello world functions.

I guess I wrote my R “hello world!” function 7 or 8 years ago while approaching R for the first time. And it is too little to illustrate the basic syntax of a programming language for a working program to a wannabe R programmer. Thus, here follows a collection of basic functions that may help a bit more than the famed piece of code.

##################################################################### Hello world functions ######################################################################################################### General infofun <- function( arguments ) { body }##################################foo.add <- function(x,y){  x+y}foo.add(7, 5)----------------------------------foo.above <- function(x){  x[x>10]}foo.above(1:100)----------------------------------foo.above_n <- function(x,n){  x[x>n]}foo.above_n(1:20, 12)----------------------------------foo = seq(1, 100, by=2)foo.squared = NULLfor (i in1:50 ) {  foo.squared[i] = foo[i]^2}foo.squared----------------------------------a <- c(1,6,7,8,8,9,2)s <- 0for (i in1:length(a)){  s <- s + a[[i]]}s----------------------------------a <- c(1,6,7,8,8,9,2,100)s <- 0i <- 1while (i <= length(a)){  s <- s + a[[i]]  i <- i+1}s----------------------------------FunSum <- function(a){  s <- 0  i <- 1  while (i <= length(a)){    s <- s + a[[i]]    i <- i+1  }  print(s)}FunSum(a)-----------------------------------SumInt <- function(n){  s <- 0  for (i in1:n){    s <- s + i  }  print(s)  }SumInt(14)-----------------------------------# find the maximum# right to left assignmentx <- c(3, 9, 7, 2)# trick: it is necessary to use a temporary variable to allow the comparison by pairs of# each number of the sequence, i.e. the process of comparison is incremental: each time# a bigger number compared to the previous in the sequence is found, it is assigned as the# temporary maximum# Since the process has to start somewhere, the first (temporary) maximum is assigned to be# the first number of the sequencemax <- x[1]for(i in x){  tmpmax = i  if(tmpmax > max){    max = tmpmax  }}maxx <- c(-20, -14, 6, 2)x <- c(-2, -24, -14, -7)min <- x[1]for(i in x){  tmpmin = i  if(tmpmin < min){    min = tmpmin  }}min----------------------------------# n is the nth Fibonacci number# temp is the temporary variableFibonacci <- function(n){  a <- 0  b <- 1  for(i in1:n){    temp <- b    b <- a    a <- a + temp  }  return(a)}Fibonacci(13)----------------------------------# R available factorial functionfactorial(5)# recursive function: ffff <- function(x) {  if(x<=0) {    return(1)  } else {    return(x*ff(x-1)) # function uses the fact it knows its own name to call itself  }}ff(5)----------------------------------say_hello_to <- function(name){  paste("Hello", name)} say_hello_to("Roberto")----------------------------------foo.colmean <- function(y){  nc <- ncol(y)  means <- numeric(nc)  for(i in1:nc){    means[i] <- mean(y[,i])  }  means}foo.colmean(airquality)----------------------------------foo.colmean <- function(y, removeNA=FALSE){  nc <- ncol(y)  means <- numeric(nc)  for(i in1:nc){    means[i] <- mean(y[,i], na.rm=removeNA)  }  means}foo.colmean(airquality, TRUE)----------------------------------foo.contingency <- function(x,y){  nc <- ncol(x)  out <- list()   for (i in1:nc){    out[[i]] <- table(y, x[,i])   }  names(out) <- names(x)  out}set.seed(123)v1 <- sample(c(rep("a", 5), rep("b", 15), rep("c", 20)))v2 <- sample(c(rep("d", 15), rep("e", 20), rep("f", 5)))v3 <- sample(c(rep("g", 10), rep("h", 10), rep("k", 20)))data <- data.frame(v1, v2, v3)foo.contingency(data,v3)

That’s all folks!

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