如何為列b的所有元素復制列a的每個元素？

Question

我有一個包含以下列的數據框：

月：字符串

名稱：字符串

計數：數字。

我想使用month列並復制不同月份中的所有名稱，以便知道計數為0的原因，因為在數據集中，如果名稱沒有計數，則不會記錄日期。

可重現的示例：

test <- data.frame(month = c("Jan","Feb","Mar","Apr","Jan","Mar","Apr"), name = c("A","A","A","A","B","B","B"), count = c(1,4,5,7,3,2,5))

# Desired result

testresult <- data.frame(month = c("Jan","Feb","Mar","Apr","Jan","Feb","Mar","Apr"), name = c("A","A","A","A","B","B","B","B"), count = c(1,4,5,7,3,0,2,5))

Answer 1

我們可以使用expand.grid與merge

 merge(expand.grid(lapply(test[1:2], unique)), test, all.x=TRUE)

Answer 2

# this may do what you want
# Create intermediate date frame with NA in missing counts
t1 <- reshape(test, idvar = "month", timevar = "name", direction = "wide")
# Create result data frame with original formats, and NA's included
testresult <- 
   reshape(t1, idvar = "month", timevar = "name", direction = "long")