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Extract a particular level from factor column in an R data frame.
To extract a particular level from factor column in an R data frame, we can use levels function with the number of the factor.
For Example, if we have a data frame called df that contains a factor column say F then we can find the third level in F by using the below given command −
levels(df$F)[2]
Example 1
Following snippet creates a sample data frame −
Grp<-factor(sample(LETTERS[1:4],20,replace=TRUE)) df1<-data.frame(Grp) df1
The following dataframe is created
Grp 1 D 2 C 3 C 4 D 5 B 6 C 7 D 8 A 9 B 10 C 11 B 12 C 13 B 14 B 15 C 16 A 17 C 18 B 19 B 20 D
To find the second level in Grp column of df1 on the above created data frame, add the following code to the above snippet −
Grp<-factor(sample(LETTERS[1:4],20,replace=TRUE)) df1<-data.frame(Grp) levels(df1$Grp)[2]
If you execute all the above given snippets as a single program, it generates the following Output −
[1] "B"
To find the fourth level in Grp column of df1 on the above created data frame, add the following code to the above snippet −
Grp<-factor(sample(LETTERS[1:4],20,replace=TRUE)) df1<-data.frame(Grp) levels(df1$Grp)[4]
If you execute all the above given snippets as a single program, it generates the following Output −
[1] "D"
Example 2
Following snippet creates a sample data frame −
Class<-factor(sample(c("First","Second","Third"),20,replace=TRUE))
df2<-data.frame(Class)
df2The following dataframe is created
Class 1 Third 2 Second 3 First 4 Third 5 Third 6 Third 7 First 8 Third 9 Third 10 Second 11 Third 12 First 13 Second 14 First 15 First 16 Third 17 First 18 First 19 Third 20 Second
To find the second level in Class column of df2 on the above created data frame, add the following code to the above snippet −
Class<-factor(sample(c("First","Second","Third"),20,replace=TRUE))
df2<-data.frame(Class)
levels(df2$Class)[2]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "Second"
To find the first level in Class column of df2 on the above created data frame, add the following code to the above snippet −
Class<-factor(sample(c("First","Second","Third"),20,replace=TRUE))
df2<-data.frame(Class)
levels(df2$Class)[1]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "First"
To find the third level in Class column of df2 on the above created data frame, add the following code to the above snippet −
Class<-factor(sample(c("First","Second","Third"),20,replace=TRUE))
df2<-data.frame(Class)
levels(df2$Class)[3]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "Third"
Example 3
Following snippet creates a sample data frame −
Category<-factor(sample(c("Low","Medium","High"),20,replace=TRUE))
df3<-data.frame(Category)
df3The following dataframe is created
Category 1 Low 2 Medium 3 Medium 4 Medium 5 Low 6 High 7 Low 8 Medium 9 Low 10 High 11 High 12 Medium 13 High 14 Medium 15 Medium 16 High 17 Low 18 High 19 High 20 Low
The levels will be sorted alphabetically hence the levels will be extracted based on first alphabet.
To find the first level in Category column of df3 on the above created data frame, add the following code to the above snippet −
Category<-factor(sample(c("Low","Medium","High"),20,replace=TRUE))
df3<-data.frame(Category)
levels(df3$Category)[1]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "High"
To find the second level in Category column of df3 on the above created data frame, add the following code to the above snippet −
Category<-factor(sample(c("Low","Medium","High"),20,replace=TRUE))
df3<-data.frame(Category)
levels(df3$Category)[2]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "Low"
To find the third level in Category column of df3 on the above created data frame, add the following code to the above snippet −
Category<-factor(sample(c("Low","Medium","High"),20,replace=TRUE))
df3<-data.frame(Category)
levels(df3$Category)[3]If you execute all the above given snippets as a single program, it generates the following Output −
[1] "Medium"
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