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("Height", "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]