dplyr，分组依据和变异-错误的结果大小

Question

Here is my example:

col_1 <- c('a','a','a','b','b')
col_4 <- c('h','h','k','t','t')
col_2 <- c('2015-10-10','2016-10-10','2015-10-10','2016-10-10','2016-10-10')
col_3 <- c(1,2,3,445,56)
test_df <- data.frame(col_1,col_2, col_3, col_4)


df_result <- test_df %>% group_by(.dots = c('col_1', 'col_4')) %>% mutate(result_col = max(col_3))

It produces the following error message:

Error in mutate_impl(.data, dots) : 
  wrong result size (2), expected 5 or 1

Could you help me to understand what I am doing wrong?

Answer 1

用这个：

df_result <- test_df %>% group_by(col_1, col_4) %>% mutate(result_col = max(col_3))

Answer 2

If, for some reason, you want to pass quoted column names, you'll have to use group_by_ instead of group_by . Note _ at the end of the function.

You can use all the dplyr verbs in similar fashion.