[R] aggregate() 함수

aggregate() 함수는 데이터의 통계량을 계산해주는 함수이다.

• Splits the data into subsets, computes summary statistics for each, and returns the result in a convenient form.

 

• 함수의 기본 형태

# 'data.frame'
aggregate(data, by, FUN, ...)

# 'formula'
aggregate(formula, data, FUN, ...)

by	a list of grouping elements, each as long as the variable in the data frame x. The elements are coerced to factors before use.
FUN	a function to compute the summary statistics which can be applied to all data subsets.
formula	a formula, such as y ~ x or cbind(y1, y2) ~ x1 + x2, where the y variables are numeric data to be split into groups according to the grouping x variables.

 

• 함수 활용 예시

# 'data.frame'
aggregate(x = testDF, by = list(fby1, fby2), FUN = "mean")

# 'formula'
aggregate(weight ~ feed, data = chickwts, mean)  # one ~ one
aggregate(breaks ~ wool + tension, data = warpbreaks, mean)  # one ~ many
aggregate(cbind(Ozone, Temp) ~ Month, data = airquality, mean)  # many ~ many

## Dot notation
### Species를 기준으로 다른 모든 컬럼의 평균값 구하기
aggregate(. ~ Species, data = iris, mean)
### len을 제외한 다른 모든 컬럼을 기준으로 len의 평균 구하기
aggregate(len ~ ., data = ToothGrowth, mean)