Data Frame in R

What is DataFrame

• one of the main tools for data analysis with R
• multiple types of data (more general than matrices)

Basic Operation

• dim()
• nrow()
• ncol()
• ...
• str()
• summary()

Data Input and Output with R

Input .csv file

• read.csv(file_path)
• read.table(file_path)
• fread(file_path)
• watchout your path!

Input excel file

• install the package (open as admin)

  • install.packages('readxl',repos="http://cran.rstudio.com/")

  • ​library(readxl)

• excel_sheets(file)
• read_excel(file, sheet = sheet)

Output to csv

write.csv(df, file = file_name)

Output to excel

1. install package "xlsx"
2. install java for 64 bit

Sys.setenv(JAVA_HOME='C:\\Program Files\\Java\\jre7') # for 64-bit version
Sys.setenv(JAVA_HOME='C:\\Program Files (x86)\\Java\\jre7') # for 32-bit version
library(xlsx)

write.xlsx(df, file = file_name)

Logical Operators and Control Flow

Logical Operators

• ==
• !=
• >=
• <=
• >
• <
• %in%
• &
• |
• &&
• ||

Control Flow (1/3) - if else

if (condition) {
    # do something ...
}

if (cond.) {
    # do something ...
} else {
    # do the other ...
}

if (cond.) {
    # do something ...
} else if (cond. 2) {
    # do another ...
} else if (cond. 3) {
    # do another ...
} else {
    # do another ...
}

if (condition) { ... } [ else if ] ... [ else ]

Control Flow (2/3) - while

while (condition) {
    # do something ...
}

while (condition) {
    # do something ...
    ...
    break
}

while (condition) { ... }

Control Flow (3/3) - for

my_vec <- c(1,2,3,4,5)
for (temp_var in vec){
    print(temp_var)
}
for (i in 1:length(vec)){
    print(vec[i])
}

for ( ... ) {
    ...
    break
    ...
    next
}

for (temporary_variable in object) { ... }