在R中使用选择功能错误

问题描述

我想获得用户最常播放的歌曲。在csv文件中我想要的三个字段是userId，songId和playCount，但是select函数给出一个错误：

I want to get the song that user's play most frequently. The three fields I want in the csv file are userId,songId and playCount but the select function is giving an error:

 c 每个组

A more suitable dplyr function in this case is filter. Here we select rows where the condition playCount == max(playCount) is TRUE within each group.
df %.%
  group_by(userId) %.%
  filter(
    playCount == max(playCount))

# Source: local data frame [5 x 3]
# Groups: userId
# 
#   userId songId playCount
# 1      A   568r        85
# 2      C    34n        18
# 3      E   454j        65
# 4      D   663a        72
# 5      B    35d        84
你会发现几个很好的。
You find several nice dplyr examples here.
                        
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