如何合并具有公共标识符的行并将新列中的出现次数求和

Question

我有以下数据：

CustomerNumber | LogEntry
1                2016-02-03
1                2016-02-05
1                2016-02-07
2                2016-02-05
2                2016-02-07

我希望它总结如下：

CustomerNumber | Frequency
1                3
2                2

我找到了解决它的方法，但它感觉不是很优雅(我是新手(。

customer_log <- active_sessions
unique <- unique(customer_log$customer_number)
session_starts = character()
customer_number = character()
for (i in 1:length(unique)) {
  session_starts[i] <- nrow(na.omit(customer_log[customer_log$customer_number == unique[i],]))
  customer_number[i] <- unique[i]
}
active_sessions = data.frame(session_starts, customer_number)

有

没有人对如何更好地解决这个问题有建议？非常感谢。

Answer 1

您可以使用

sqldf包轻松实现此目的。

library(sqldf)
sqldf("SELECT CustomerNumber, count(*) AS Frequency FROM df GROUP BY CustomerNumber")