按组 ID 对 data.table 中的行进行简单扩展

Question

对于以下给定的数据集：

> df <- data.table(ID=LETTERS[1:4],y_min=c(1970,1973,1976,1971),y_max=c(1974,1975,1980,1974))
> df
   ID y_min y_max
1:  A  1970  1974
2:  B  1973  1975
3:  C  1976  1980
4:  D  1971  1974

ID代表企业ID，y_min和y_max是企业数据出现在数据集中的第一年和最后一年。

如何通过创建一个包含最小和最大年份之间的所有年份的新列“年”来扩展行（按每个公司），因此生成以下内容：

> df
    ID y_min y_max year
 1:  A  1970  1974 1970
 2:  A  1970  1974 1971
 3:  A  1970  1974 1972
 4:  A  1970  1974 1973
 5:  A  1970  1974 1974
 6:  B  1973  1975 1973
 7:  B  1973  1975 1974
 8:  B  1973  1975 1975
 9:  C  1976  1980 1976
10:  C  1976  1980 1977
11:  C  1976  1980 1978
12:  C  1976  1980 1979
13:  C  1976  1980 1980
14:  D  1971  1974 1971
15:  D  1971  1974 1972
16:  D  1971  1974 1973
17:  D  1971  1974 1974

提前致谢！

Answer 1

一种选择是通过对“ID”列进行分组来创建list 列，然后在“y_min”、“y_max”和unnest 之间执行:（来自tidyr）@987654325 @专栏

library(data.table)
library(tidyr)
df[, year := .(list(y_min:y_max)), ID]
df %>%
    unnest(c(year))

-输出

# A tibble: 17 x 4
#   ID    y_min y_max  year
#   <chr> <dbl> <dbl> <int>
# 1 A      1970  1974  1970
# 2 A      1970  1974  1971
# 3 A      1970  1974  1972
# 4 A      1970  1974  1973
# 5 A      1970  1974  1974
# 6 B      1973  1975  1973
# 7 B      1973  1975  1974
# 8 B      1973  1975  1975
# 9 C      1976  1980  1976
#10 C      1976  1980  1977
#11 C      1976  1980  1978
#12 C      1976  1980  1979
#13 C      1976  1980  1980
#14 D      1971  1974  1971
#15 D      1971  1974  1972
#16 D      1971  1974  1973
#17 D      1971  1974  1974

---

或者只使用data.table

df[, year := Map(`:`, y_min, y_max)]
df[rep(seq_len(.N), lengths(year))][, year := unlist(df$year)][]

-输出

#     ID y_min y_max year
# 1:  A  1970  1974 1970
# 2:  A  1970  1974 1971
# 3:  A  1970  1974 1972
# 4:  A  1970  1974 1973
# 5:  A  1970  1974 1974
# 6:  B  1973  1975 1973
# 7:  B  1973  1975 1974
# 8:  B  1973  1975 1975
# 9:  C  1976  1980 1976
#10:  C  1976  1980 1977
#11:  C  1976  1980 1978
#12:  C  1976  1980 1979
#13:  C  1976  1980 1980
#14:  D  1971  1974 1971
#15:  D  1971  1974 1972
#16:  D  1971  1974 1973
#17:  D  1971  1974 1974

---

或自加入

df[df, .(y_min, y_max, year = y_min:y_max), on = .(ID), by = .EACHI]