R Notebook

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1. Creating and printing data frames

kids <- c("Alex","Liza")
ages <- c(9,7)
ka <- data.frame(kids,ages,stringsAsFactors=FALSE)
ka # matrix-like viewpoint

2. Exploring DF

ka[[1]]

## [1] "Alex" "Liza"

ka$kids

## [1] "Alex" "Liza"

ka[,1]

## [1] "Alex" "Liza"

str(ka)

## 'data.frame':    2 obs. of  2 variables:
##  $ kids: chr  "Alex" "Liza"
##  $ ages: num  9 7

3.Extract subdata frames by rows or columns

getwd()

## [1] "C:/1rdata"

setwd("C:/1rdata")
examsquiz <- read.csv("examsquiz.csv",sep=",",header=TRUE)

head(examsquiz)

examsquiz[1:3,] #extract rows

examsquiz[1:3,2] #extract values for rows ... in column ... 

## [1] 3.3 3.2 2.0

class(examsquiz[1:3,2])

## [1] "numeric"

examsquiz[2:5,2,drop=FALSE] #keep it as a onecolumn DF (default vector due to the fact that 1 line only)

examsquiz[examsquiz$Exam1 >= 3,] #filtering to extract the subframe

4. Treatment of NA Values

x <- c(20,400,NA)
mean(x)

## [1] NA

mean(x,na.rm=TRUE)

## [1] 210

5. Apply subset() function to DF for row selection

examsquiz[examsquiz$Exam1 >= 2,] #way_1 

subset(examsquiz,Exam1 >= 2) #way_2, using 'subset()' function