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R: data frames

An R data frame roughly corresonds to a SAS (or SPSS) data set.

A data frame is stored as a list of vectors, factors and/or matrices each of which has the same length (i. e. tabular data)

Dimensions

The dimensions of a data frame can be queried with nrow() and length().

nrow() returns the number of observations (or rows or records).

length() returns the number of columns.

df <- data.frame (
  val_1 = c('foo', 'bar', 'baz'),
  val_1 = c(   1 ,    2 ,    3 )
)

nrow  (df) # 3
length(df) # 2

A data.frame's class is data.frame; typeof() and mode() return list.

df <- data.frame (
  val_1 = c('foo', 'bar', 'baz'),
  val_1 = c(   1 ,    2 ,    3 )
)

class (df) # data.frame
typeof(df) # list
mode  (df) # list

Some functions to create data frames and values to it are (TO BE COMPLETED):

read.csv() to read a CSV file into a data frame
read.csv(…, text = "") to assign data that is stored within an R source/script file
…