Factors are
used to represent categorical data. Factors in R are stored as a vector of
integer values with a corresponding set of character values to use when the
factor is displayed. By using factor() function, you can create a factor.
There are
two types of factors
a. ordered
b. unordered
Factors
represent a very efficient way to store character values, because each unique
character value is stored only once, and the data itself is stored as a vector
of integers.
> months <- c("January", "February", "March", "April", "May", "June", "July","August", "January", "March", "september", "April", "June", "May", "June") > monthsFact <- factor(months) > > monthsFact [1] January February March April May June July August January March september April June May June Levels: April August February January July June March May september > > table(monthsFact) monthsFact April August February January July June March May september 2 1 1 2 1 3 2 2 1
As
you observe above output, months are not displayed in order. If you want to
display months in order, create ordered factor.
> monthsFact <- factor(months, levels=c("January","February","March", "April","May","June","July","August","September", "October","November","December"),ordered=TRUE) > > monthsFact [1] January February March April May June July August January March <NA> April June May June Levels: January < February < March < April < May < June < July < August < September < October < November < December > > table(monthsFact) monthsFact January February March April May June July August September October November December 2 1 2 2 2 3 1 1 0 0 0 0 >
References
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