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How to find the mean based on single group value in an R data frame?
To find the mean based on single group value in an R data frame, we can use mean function with subsetting through single square brackets.
For example, if we have a data frame called df that contains a categorical column say C having three groups Low, Medium, High and a numerical column say Num then mean of Num for Medium group can be found by using the command given below −
mean(df$C[df$Num=="Medium"])
Example 1
Following snippet creates a sample data frame −
Group<-sample(LETTERS[1:4],20,replace=TRUE) Score<-rpois(20,5) df1<-data.frame(Group,Score) df1
The following dataframe is created −
Group Score 1 D 7 2 D 6 3 D 3 4 B 5 5 C 7 6 A 2 7 D 7 8 D 5 9 C 1 10 C 6 11 C 9 12 D 3 13 C 6 14 B 8 15 C 2 16 B 6 17 D 7 18 C 8 19 A 12 20 B 3
To get the mean of Score for group A, add the following code to the above snippet −
Group<-sample(LETTERS[1:4],20,replace=TRUE) Score<-rpois(20,5) df1<-data.frame(Group,Score) mean(df1$Score[df1$Group=="A"])
Output
If you execute all the above given snippets as a single program, it generates the following output −
[1] 7
Example 2
Following snippet creates a sample data frame −
Class<-sample(c("I","II","III"),20,replace=TRUE)
Price<-sample(10:20,20,replace=TRUE)
df2<-data.frame(Class,Price)
df2The following dataframe is created −
Class Price 1 II 19 2 I 15 3 I 14 4 I 19 5 III 13 6 I 17 7 III 12 8 I 10 9 II 18 10 II 11 11 II 13 12 I 11 13 II 12 14 III 11 15 II 13 16 II 15 17 III 10 18 I 17 19 III 18 20 I 14
To get the mean of Price for Class I, add the following code to the above snippet −
Class<-sample(c("I","II","III"),20,replace=TRUE)
Price<-sample(10:20,20,replace=TRUE)
df2<-data.frame(Class,Price)
mean(df2$Price[df2$Class=="I"])Output
If you execute all the above given snippets as a single program, it generates the following output: −
[1] 14.625
Example 3
Following snippet creates a sample data frame −
Category<-sample(c("First","Second","Third","Fourth"),20,replace=TRUE)
Sales<-sample(10:50,20)
df3<-data.frame(Category,Sales)
df3The following dataframe is created −
Category Sales 1 First 49 2 Fourth 43 3 Second 44 4 Third 35 5 Fourth 21 6 Third 50 7 First 45 8 Fourth 15 9 Second 20 10 First 11 11 First 17 12 Fourth 37 13 Third 48 14 Second 32 15 Fourth 10 16 Fourth 38 17 First 40 18 First 22 19 Second 25 20 First 47
To get the mean of Sales for group First, add the following code to the above snippet −
Category<-sample(c("First","Second","Third","Fourth"),20,replace=TRUE)
Sales<-sample(10:50,20)
df3<-data.frame(Category,Sales)
mean(df3$Sales[df3$Category=="First"])Output
If you execute all the above given snippets as a single program, it generates the following output: −
[1] 33
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