Practical Data Wrangling

Indexing R dataframes

Individual columns can be selected from a dataframe using the $ symbol. The following selects the data from 2011 from the roads dataframe:

roads.2011 = roads$X2011

The resulting value is an R vector containing the values of the selected column. 

Dataframes can also be indexed by row and column using the following syntax:

new.dataframe <- original.dataframe[<row_index>,<column index>].

To select all rows or all columns, the row_index or column_index can be left blank. For example:

the.same.thing <- roads[,]

The rows and columns indices can both be an integer value or a vector of integer values. For example:

first.three.rows <- roads[1:3,]first.three.columns <- roads[,1:3]

Row and column indices can also be a vector of ...