排序表的唯一参数

Question

我有一个名为myTable(输入)的表:

 user_name   session_num  
1     "Joe"            1    
2     "Tom"            2    
3    "Fred"            1    
4     "Tom"            1    
5     "Joe"            2    
6     "John"           1 

我想知道我user_id有多少 只有 session_num = 1(输出):

   user_name   session_num   
1     "Fred"             1
2     "John"             1

Answer 1

这是一个可能的解决方案 data.table

library(data.table)
setDT(df)[, if(all(session_num == 1)) .SD, by = user_name]
#    user_name session_num
# 1:      Fred           1
# 2:      John           1

另一种选择是尝试反连接

df[session_num == 1][!df[session_num != 1], on = "user_name"]
#    user_name session_num
# 1:      Fred           1
# 2:      John           1

Answer 2

一个类似的解决方案dplyr:

library(dplyr)
myTable %>%
  group_by(user_name) %>%
  filter(all(session_num == 1))

这使:

  user_name session_num
     (fctr)       (int)
1      Fred           1
2      John           1