根据 B 列中的一系列值获取 A 列的平均值

Question

My dataframe has several columns as follows:

df1 <- data.frame(A = c(1,2,4), B=c(1,3,1), C=c(1,1,3))

I have two conditions to get average values for column A.

• Condition 1: I want to get average of column A when B is 1, ie only row1 and row2 will be averaged.
• Condition 2: I want to get average of column B when column A's values are larger than 1 but smaller than 3, ie only row 2 will be considered.

I know I can use filter to cut the dataframe to have column B = 1 only. However, I am unsure how to do it when I want the column B to be considered as a range within 1 and 3.

Are there any smarter ways to get the average values of column without cutting the dataframe into a smaller size first?

Answer 1

You can do your subsetting in the same call to mean like so:

with(df1, mean(A[B == 1]))

with(df1, mean(B[A > 1 & A < 3]))

Answer 2

You can combine two logical tests with & . So you could combine the B > 1 test with B < 3 :

# Condition A:
mean(df1$A[df1$B==1])

# Condition B:
mean(df1$B[df1$A>1 & df1$A<3])