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How Do I Recode Values in R?

How Do I Recode Values in R?

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John Fox’s car library contains the recode function for recoding values of variables in a data frame. Take a hypothetical data set named food which contains information on the number of calories a person consumed over seven days. The variables in the data file are day, representing the day of the week, and calories, representing the number of calories that were consumed. The data are saved in a tab-delimited file and can thus be read into memory using the read.table command.

> food<-read.table("http//www.methodsconsultants.com/data/food.dat", 
header=TRUE, sep="t")

The data look like the following:

> food
        day calories
1    Sunday     2050
2    Monday     1800
3   Tuesday     1925
4 Wednesday     2015
5  Thursday     1875
6    Friday     3000
7  Saturday     2800

To use the recode function it is first necessary to load the car library.

> library(car)

Say the number of calories was recorded incorrectly for Monday and Tuesday. The following takes care of the recoding:

> food$calories<-recode(food$calories,"1800=2200; 1925=2000")

In the recode function, the name of the variable to be recoded is entered as the first argument. All recodes are then enclosed in a single set of double quotation marks and separated by semi-colons. Recoding factors works the same way, though it is necessary to use single quotation marks around string values. In addition, it is possible to recode multiple different values into a single new value. The following demonstrates:

> food$day<-recode(food$day, "c('Friday','Saturday','Sunday')='Weekend';
+ 	else='Weekday'")

The data now look like the following:

> food
      day calories
1 Weekend     2050
2 Weekday     2200
3 Weekday     2000
4 Weekday     2015
5 Weekday     1875
6 Weekend     3000
7 Weekend     2800

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