Chapter 6 Loop functions

lapply sapply tapply mapply apply: let’s set margins

6.1 Debbuging and error handling

message: informative
warnings: unexpected behavior, display once execution has finished
error: fatal breaks the program
condition: generic

out printing to the console

useful tools

traceback debug browser trace recover

blunt techniques insert cat/ print staments insid the function

mean(x)
traceback()

debug(lm)
lm(x-y)

undebug(lm)

optins(error=recover)
optins(error=browser)

optins(error=NULL)

tidyverse_update()

<<- is an operator used to assign a object to a different environment

6.2 R objects

6.3 Create package documentation

Run devtools::document() (or press Ctrl/Cmd + Shift + D in RStudio) to convert roxygen comments to .Rd files.

6.4 SWIRL practices

6.4.1 lapply sapply

loop functions or *apply functions

split apply combine strategy lay out by Hadley Wickham in his paper titled ‘The Split-Apply-Combine Strategy for Data Analysis’.

Rows observation and columns variables

specify its own anonymous function lapply(unique_vals, function(elem) elem[2])

back in week to we read some data from a file. Imagine we want to analyze this information we want to know what type is. first we try simply to find the class of students which ain’t very us

Now we want to iterate operation over it lapply returns a list type as a result. sapply tries to simplify whenever is possible. iF every result is of length 1 it returns a vector if they are all bigger than one and with the same length it returns a matrix.

students <- read.table("../data/student_info.csv",sep=";",header=TRUE,nrows=5)
class(students)

## [1] "data.frame"

cls<- lapply(students,class)

6.4.2 vapply and tapply

vapply allows to specify the format of the result and throughs an error if not matched.

more in depth of the source function source from web github

print(" I am filed called from a URL")

## [1] " I am filed called from a URL"

source("https://raw.githubusercontent.com/jsduenass/datasciencecoursera/master/code/hello_I_am_from_the_web.R")

## [1] "In R, the source function allows to call either files path names or URL connettion"

One can call an R script and all its content using source. R can also interface with different files compress files using … and web pages using the url function.

#remove(list=ls())
#source("code/simple_script.R", encoding = 'UTF-8')
#eval(parse("simple_script.R", encoding="UTF-8"))
#roll()
#dput(rank)
#dump(c(rank,rolls))

content <- file("../data/student_info.csv","r")
some_lines <-readLines(content,5)
print(some_lines)

## [1] "Name and Lastname; ID; email adress"                  
## [2] "Samuel Jackson; 10124585611; samuelJ@mail.com"        
## [3] "Robert Downey; 4525111559; rdownironman@mail.c"       
## [4] "Douglas Adams; 14884674721; zaphodbeeblebrox@mail.com"
## [5] "Stephen Wolfram; 74682868914; wolframalpha@mail.com"

r measure run time and optimization