How to Find Conditional Mean from one coloum

[Atmadeep_Ghoshal]

Can somebody please help me in finding the mean from the following data set of the age of people who are more than 30 years old using r

Name. Age
A 34
B. 22
C. 67
D. 43
E. 10

I'm kind of a newbie. I used the code mean(df$age) but cant set the condition to less than 30.

[FJCC]

Using base R you can do the following.

DF <- data.frame(Name = LETTERS[1:5], Age = c(34, 22, 67,43, 10))
mean(DF[DF$Age < 30, "Age"])
#> [1] 16

#Why does that work?
DF$Age < 30  #This returns TRUE and FALSE values
#> [1] FALSE  TRUE FALSE FALSE  TRUE

DF[DF$Age < 30, ] #This returns all rows where the comparison is TRUE
#>   Name Age
#> 2    B  22
#> 5    E  10

DF[DF$Age < 30, "Age"] #Tis returns just the Age column of selected rows
#> [1] 22 10

^{Created on 2021-07-08 by the reprex package (v0.3.0)}

This can be done more elegantly with the dplyr package

library(dplyr)
DF %>% filter(Age < 30) %>% summarize(AvgAge = mean(Age))

[Atmadeep_Ghoshal]

Thank you so much for your help!