Learn R – How to Extract Rows & Columns from Data Frame

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This article represents command set in R programming language, which could be used to extract rows and columns from a given data frame. When working on data analytics or data science projects, these commands come very handy in data cleaning activities.  This article is meant for beginners/rookies getting started with R and wanting to know or see examples of extracting information from a data frame. Please feel free to comment/suggest if I missed to mention one or more important points. Also, sorry for the typos.
Following are the key points described later in this article:

  • Commands to extract rows and columns
  • Command to extract a column as data frame
  • Command to extract an element

 

Suppose you have a data frame, df, which is represented such as following. Below is created a data frame consisting of three vectors that consist of information such as height, weight, age.

df <- data.frame( c( 183, 85, 40), c( 175, 76, 35), c( 178, 79, 38 ))
names(df) <- c("Hieght", "Weight", "Age")

 

Commands to Extract Rows and Columns

Following represents different commands which could be used to extract one or more row with one or more columns. Note that the output is extracted as a data frame. This could be checked using “class” command.

# All Rows and All Columns
df[,]

# First row and all columns
df[1,]

# First two rows and all columns
df[1:2,]

# First and third row and all columns
df[ c(1,3), ]

# First Row and 2nd and third column
df[1, 2:3]

# First, Second Row and Second and Third COlumn
df[1:2, 2:3]

# Just First Column with All rows
df[, 1]

# First and Third Column with All rows
df[,c(1,3)]

 

Command to Extract a Column as Data Frame

Following represents command which could be used to extract a column as a data frame. If you use command such as “df[,1]”, the output will be a numeric vector (in this case). To get an output as a data frame, you would need to use something like below.

# First Column as data frame
as.data.frame( df[,1], drop=false)

 

Command to Extract an Element

Following represents command which could be used to extract an element at a particular row and column. It is as simple as writing a row and a column number such as following:

# Element at 2nd row, third column
df[2,3]

 

Ajitesh Kumar

Ajitesh Kumar

Ajitesh has been recently working in the area of AI and machine learning. Currently, his research area includes Safe & Quality AI. In addition, he is also passionate about various different technologies including programming languages such as Java/JEE, Javascript and technologies such as Blockchain, mobile computing, cloud-native technologies, application security, cloud computing platforms, big data etc.

He has also authored the book, Building Web Apps with Spring 5 and Angular.
Ajitesh Kumar

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