Question

Problem 10.3: For each of these computations, say what R function is the most appropriate:

1.Count the number of cases in a data table.
2.List the names of the variables in a data table.
3.For data tables in an R package, display the documentation (“codebook”) for the data table.
4.Load a package into your R session.
5.Mark a data table as grouped by one or more categorical variables.

Answer 1

The appropiate R functions for the given computations are as follows:

1. for one group: nrow(data[data$group1 == "A" & data$group2 == "C", ])

for each group: aggregate(x ~ group1 + group2, data = data, FUN = length)

2. To list the names of the variables in a data table:

function name:

object()

#or

ls()

3. For data tables in an R package, display the documentation (“codebook”) for the data table:

  library(codebook)
codebook_data <- codebook::bfi

#with

  codebook_data <- rio::import("https://osf.io/s87kd/download", "csv")

4. To load a package into your R session:

.libPaths() # get library location
library()   # see all packages installed
search()    # see packages currently loaded

5. To mark a data table as grouped by one or more categorical variables

  group_by(data, category) %>%

skim()