r - 如何将缺失的 NA 包含到不平衡面板数据集的 R data.frame 中？

Question

我有一个不平衡的面板数据，我需要包含所有缺失的观察结果。例如，我有这样的事情：

         YEAR    VAR
 FIRM.1  YEAR.1  x.1
 FIRM.1  YEAR.3  x.2
 FIRM.2  YEAR.2  x.3
 FIRM.2  YEAR.3  x.4

我想添加缺少的 NA：

         YEAR    VAR
 FIRM.1  YEAR.1  x.1
 FIRM.1  YEAR.2  NA
 FIRM.1  YEAR.3  x.2
 FIRM.2  YEAR.1  NA
 FIRM.2  YEAR.2  x.3
 FIRM.2  YEAR.3  x.4  

如何最方便地做到这一点？

Answer 1

我会使用expand.gridand merge。

假设您的数据如下：

mydf <- structure(list(FIRM = c("FIRM.1", "FIRM.1", "FIRM.2", "FIRM.2"),
    YEAR = c("YEAR.1", "YEAR.3", "YEAR.2", "YEAR.3"), VAR = c("x.1", "x.2",
    "x.3", "x.4")), .Names = c("FIRM", "YEAR", "VAR"),
    class = "data.frame", row.names = c(NA, -4L))
mydf
#     FIRM   YEAR VAR
# 1 FIRM.1 YEAR.1 x.1
# 2 FIRM.1 YEAR.3 x.2
# 3 FIRM.2 YEAR.2 x.3
# 4 FIRM.2 YEAR.3 x.4

用于expand.grid创建“完整”集的“FIRM”和“YEAR”数据，然后merge.

merge(mydf, expand.grid(FIRM = unique(mydf$FIRM), 
                        YEAR = unique(mydf$YEAR)), 
      all.y = TRUE)
#     FIRM   YEAR  VAR
# 1 FIRM.1 YEAR.1  x.1
# 2 FIRM.1 YEAR.2 <NA>
# 3 FIRM.1 YEAR.3  x.2
# 4 FIRM.2 YEAR.1 <NA>
# 5 FIRM.2 YEAR.2  x.3
# 6 FIRM.2 YEAR.3  x.4