Dataframes

r-introduction

Introduction to data frames in R.

Author

Aravind Hebbali

Published

May 12, 2017

Introduction

In the previous post, we learnt about lists. In this post, we will learn about dataframe.

create dataframe
select columns
select rows
utitlity functions

Create dataframes

Use data.frame to create dataframes. Below is the function syntax:

args(data.frame)

## function (..., row.names = NULL, check.rows = FALSE, check.names = TRUE, 
##     fix.empty.names = TRUE, stringsAsFactors = default.stringsAsFactors()) 
## NULL

Data frames are basically lists with elements of equal lenght and as such, they are heterogeneous. Let us create a dataframe:

name <- c('John', 'Jack', 'Jill')
age <- c(29, 25, 27)
graduate <- c(TRUE, TRUE, FALSE)
students <- data.frame(name, age, graduate)
students

##   name age graduate
## 1 John  29     TRUE
## 2 Jack  25     TRUE
## 3 Jill  27    FALSE

Basic Information

class(students)
## [1] "data.frame"
names(students)
## [1] "name"     "age"      "graduate"
colnames(students)
## [1] "name"     "age"      "graduate"
str(students)
## 'data.frame':    3 obs. of  3 variables:
##  $ name    : chr  "John" "Jack" "Jill"
##  $ age     : num  29 25 27
##  $ graduate: logi  TRUE TRUE FALSE
dim(students)
## [1] 3 3
nrow(students)
## [1] 3
ncol(students)
## [1] 3

Select Columns

[]
[[]]
$

# using [
students[1]
##   name
## 1 John
## 2 Jack
## 3 Jill

# using [[
students[[1]]
## [1] "John" "Jack" "Jill"

# using $
students$name
## [1] "John" "Jack" "Jill"

Multiple Columns

students[, 1:3]
##   name age graduate
## 1 John  29     TRUE
## 2 Jack  25     TRUE
## 3 Jill  27    FALSE

students[, c(1, 3)]
##   name graduate
## 1 John     TRUE
## 2 Jack     TRUE
## 3 Jill    FALSE

Select Rows

# single row
students[1, ]
##   name age graduate
## 1 John  29     TRUE

# multiple row
students[c(1, 3), ]
##   name age graduate
## 1 John  29     TRUE
## 3 Jill  27    FALSE

If you have observed carefully, the column names has been coerced to type factor. This happens because of a default argument in data.frame which is stringsAsFactors which is set to TRUE. If you do not want to treat it as factors, set the argument to FALSE.

students <- data.frame(name, age, graduate, stringsAsFactors = FALSE)

We will learn about wrangling dataframes in a different post.