Question

I have a data.frame in R. I want to create three different data.frame using a loop and subset function. I have a large data.frame, but what I need is in the example below:

sex<-c("M","M","M","F","M","F")
age<-c(20,18,17,20,18,17)
name<-c("John", "Joseph", "Bill", "Sarah", "Robert", "Dana")
data<-data.frame(sex, age, name)

>data
        sex  age   name
    1   M    20    John
    2   M    18    Joseph
    3   M    17    Bill
    4   F    20    Sarah
    5   M    18    Robert
    6   F    17    Dana

What I want is:

>age17
      sex   age   name
    1 M     17    Bill
    2 F     17    Dana

>age18
      sex   age   name
    1 M     18    Joseph
    2 M     18    Robert


>age20
      sex   age   name
    1 M     20    John
    2 F     20    Sarah

I can use the commands below:

>age17<-subset(data, data[,2]==17)
>age18<-subset(data, data[,2]==18)
>age20<-subset(data, data[,2]==20)

But it is possible to use a loop to reduce the size of commands?

Answer 1

Use split:

x <- split(data, data$age)

x
$`17`
  sex age name
3   M  17 Bill
6   F  17 Dana

$`18`
  sex age   name
2   M  18 Joseph
5   M  18 Robert

$`20`
  sex age  name
1   M  20  John
4   F  20 Sarah

---

You now have a list of data frames, and you can access the elements of the list using any of the extract operators, i.e. $, [ or [[.

For example, the first element:

x[1]
$`17`
  sex age name
3   M  17 Bill
6   F  17 Dana

Or the element with name 17. But notice that you have to use backticks to refer to these names, since names starting with numerals are not standard:

x$`17`
  sex age name
3   M  17 Bill
6   F  17 Dana