Convert Tidy data & Untidy data in R

※ Convert in R

# tidyverse 패키지 설치 및 불러오기
install.packages("tidyverse")
library(tidyverse)

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예시 1.

#  Untidy data 생성
stu1 <- data.frame(name = c('Jimin', 'Hyunsoo', 'Sangho', 'Yerim'),
                    year1 = c(100, 70, 80, 60),
                    year2 = c(77, 49, 53, 82))

1. Convert “Untidy Data” to “Tidy Data”

# pivot_longer 함수 이용
# pivot_longer(data, cols, names_to, values_to)
stu1_long <- pivot_longer(stu1, 
                          cols = c('year1', 'year2'),
                          names_to='year', 
                          values_to = 'math')

# gather 함수 이용
# gather(data, key, value, colA, colB, ...)
stu1_long <- gather(stu1,
                    key = year,
                    value = math,
                    year1, year2)

2. Convert “Tidy Data” to “Untidy Data”

# pivot_wider 함수 이용
# pivot_wider(data, names_from, values_from)
stu1_wide <- pivot_wider(stu1_long,
                        names_from = year,
                        values_from = math)

# spread 함수 이용
# spread(data, key, value)
stu1_wide <- spread(stu1_long,
                    key = year,
                    value = math)

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예시 2.

# Tidy data 생성
stu2 <- data.frame(id = rep(1:3, each = 4),
                   name = rep(c('Jimin', 'Hyunsoo', 'Sangho'), each = 4),
                   year = rep(2020:2021, each = 2),
                   term = rep(1:2, rep = 2),
                   math = c(86, 66, 67, 93, 97, 63, 58, 89, 95, 65, 64, 60),
                   eng = c(79, 84, 92, 73, 82, 89, 90, 75, 83, 74, 95, 71))

Convert “Tidy Data” to “Untidy Data”

# 년도, 학기별로 수학, 영어 점수
pivot_wider(stu2, 
            names_from = c("year","term"),
            values_from = c("math", "eng"))

pivot_wider(stu2, 
            names_from = "year",
            values_from = c("math", "eng"))

# 수학 점수만 년도, 학기별
pivot_wider(stu2[1:5], 
            names_from = c("year","term"),
            values_from = "math")

# 영어 점수만 년도, 학기별
# %>%를 활용하여 math열 제외
stu2 %>%
  select(-math) %>%
  pivot_wider(names_from = c("year","term"),
              values_from = "eng")

# 년도별 수학 점수 평균
stu2 %>%
  group_by(id, name, year) %>%
  summarize(avg_math = mean(math)) %>%
  pivot_wider(names_from = "year",
              values_from = "avg_math")