R：dplyr重复的列名

Question

我有一个大型数据集，如下所示：

df1 <- data.frame(matrix(vector(),ncol=4, nrow = 3))
colnames(df1) <- c("Date","A","B","C")
df1[1,] <- c("2000-01-30","0","1","0")
df1[2,] <- c("2000-01-31","2","0","3")
df1[3,] <- c("2000-02-29","1","2","1")
df1[4,] <- c("2000-03-31","2","1","3")
df1
        Date  A  A  C
1 2000-01-30  0  1  0
2 2000-01-31  2  0  3
3 2000-02-29  1  2  1
4 2000-03-31  2  1  3

我想要：

        Date  A  A  C
1    2000-01  2  1  3
2    2000-02  1  2  1
3    2000-03  2  1  3

这是我做的：

library(zoo)
library(dplyr)
df1[,-1] = lapply(df1[,-1], as.numeric)
df1 %>% mutate(Date = as.yearmon(Date)) %>%
group_by(Date) %>%
summarise_each(funs(sum))

当没有重复的列名时，这很有用。但是，根据数据的大小，某些列可能具有相同的名称，从而导致错误found duplicated column name: A。我不想组合列，我想得到如上所述的结果。请指教。