R - 对多行数据帧执行 CountIF

Question

我在谷歌上搜索了很多关于如何在 R 中执行 CountIF 的示例，但是我仍然没有找到我想要的解决方案。

我基本上有 2 个数据帧：

df1: customer_id | date_of_export - here, we have only 1 date of export per customer
df2: customer_id | date_of_delivery - here, a customer can have different delivery dates (which means, same customer will appear more than once in the list)

而且我需要计算 df1 中的每个 customer_id，他们在出口日期之后收到了多少次交货。所以，我需要 count if df1$customer_id = df2$customer_id AND df1$date_of_export <= df2$date_of_delivery

更好地理解：

customer_id | date_of_export
1 | 2018-01-12
2 | 2018-01-12
3 | 2018-01-12

customer_id | date_of_delivery
1 | 2018-01-10
1 | 2018-01-17
2 | 2018-01-13
2 | 2018-01-20
3 | 2018-01-04

我的输出应该是：

customer_id | date_of_export | deliveries_after_export
1 | 2018-01-12 | 1 (one delivery after the export date)    
2 | 2018-01-12 | 2 (two deliveries after the export date)
3 | 2018-01-12 | 0 (no delivery after the export date)

似乎没有那么复杂，但我没有找到一个好的方法来做到这一点。苦苦挣扎了2天，一事无成。

我希望我在这里说清楚了。谢谢！

Answer 1

我建议将两个 data.frames 合并在一起，这样就很简单 sum():

library(data.table)
df3 <- merge(df1, df2)
setDT(df3)[, .(deliveries_after_export = sum(date_of_delivery > date_of_export)), by = .(customer_id, date_of_export)]

#   customer_id date_of_export deliveries_after_export
#1:           1     2018-01-12                       1
#2:           2     2018-01-12                       2
#3:           3     2018-01-12                       0

R - 对多行数据帧执行 CountIF

R - Performing a CountIF for a multiple rows data frame

r

countif