根据来自两列的信息合并两个数据集

Question

我有两个这样的大型数据集：

df1 <- data.frame(subject = c(rep(1, 15), rep(2, 14)), day =c(0,0,1,1,1,2,3,15,15,16,16,17,17,18,19,0,0,1,1,2,3,15,15,16,16,17,17,18,19),stime=c('4/16/2012 6:25','4/16/2012 7:01','4/17/2012 7:22','4/17/2012 7:45','4/17/2012 8:13','4/18/2012 6:50','4/19/2012 6:55','5/1/2012 6:28','5/1/2012 7:00','5/2/2012 6:28','5/2/2012 7:00','5/3/2012 6:22','5/3/2012 7:00','5/4/2012 6:26','5/5/2012 6:47','4/23/2012 5:56','4/23/2012 6:30','4/24/2012 6:55','4/24/2012 7:20','4/25/2012 6:32','4/26/2012 6:28','5/8/2012 5:54','5/8/2012 6:30','5/9/2012 5:55','5/9/2012 6:30','5/10/2012 5:55','5/10/2012 6:30','5/11/2012 6:41','5/12/2012 6:46'))

df2 <- data.frame(subject = c(rep(1, 10), rep(2, 10)), day =c(1,1,2,3,9,12,15,15,16,17,1,1,2,3,9,13,15,15,16,17),dtime=c('4/17/2012 7:15','4/17/2012 7:15','4/17/2012 7:15','4/17/2012 7:15','4/25/2012 7:15','4/28/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','4/24/2012 6:45','4/24/2012 6:45','4/24/2012 6:45','4/24/2012 6:45','5/2/2012 7:00','5/6/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45'))

...

我想合并两个数据集，使df2中的'dtime'可以匹配df1中的'subject'和'day'，并用'.'填写缺失值。在 df1 中，行号应与 df1 相同。预期的输出应如下所示：

merged <- data.frame(subject = c(rep(1, 15), rep(2, 14)), day =c(0,0,1,1,1,2,3,15,15,16,16,17,17,18,19,0,0,1,1,2,3,15,15,16,16,17,17,18,19),stime=c('4/16/2012 6:25','4/16/2012 7:01','4/17/2012 7:22','4/17/2012 7:45','4/17/2012 8:13','4/18/2012 6:50','4/19/2012 6:55','5/1/2012 6:28','5/1/2012 7:00','5/2/2012 6:28','5/2/2012 7:00','5/3/2012 6:22','5/3/2012 7:00','5/4/2012 6:26','5/5/2012 6:47','4/23/2012 5:56','4/23/2012 6:30','4/24/2012 6:55','4/24/2012 7:20','4/25/2012 6:32','4/26/2012 6:28','5/8/2012 5:54','5/8/2012 6:30','5/9/2012 5:55','5/9/2012 6:30','5/10/2012 5:55','5/10/2012 6:30','5/11/2012 6:41','5/12/2012 6:46'),dtime =c('.','.','4/17/2012 7:15','4/17/2012 7:15','4/17/2012 7:15','4/17/2012 7:15','4/17/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','5/1/2012 7:15','.','.','.','.','4/24/2012 6:45','4/24/2012 6:45','4/24/2012 6:45','4/24/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','5/8/2012 6:45','.','.'))

...

我尝试使用merge(df1, df2, by = c('subject', 'day'))，但效果不佳，它产生了我不想要的额外行。

有人知道实现这一点吗？

Answer 1

这似乎行得通。

result <- merge(df1,unique(df2),by=c("subject","day"),all.x=T)
result$dtime <- as.character(result$dtime)
result[is.na(result$dtime),]$dtime="."

一些注意事项：

1. 您不需要 merge(...) 中的 by=... 参数，因为默认情况下是合并所有常用列（在您的情况下是 subject 和 day）。为了清楚起见，我将其包括在内。
2. 另一个答案产生了额外的列，因为df2 中的某些行是重复的。在这种情况下，我们可以使用unique(...) 处理它，但通常这是一个更大问题的症状。你真的应该看看为什么会有重复的行......
3. 设置方式，dtime 是一个因素。您必须先将其转换为字符，然后才能将 NA 设置为其他值。

最后，如果您的数据集确实很大（数百万行），那么请考虑使用数据表。这将快得多。

library(data.table)
dt1 <- data.table(df1,key="subject,day")
dt2 <- data.table(unique(df2),key="subject,day")
result <- dt2[dt1]
result[is.na(dtime),dtime:="."]
head(result)
#    subject day          dtime          stime
# 1:       1   0              . 4/16/2012 6:25
# 2:       1   0              . 4/16/2012 7:01
# 3:       1   1 4/17/2012 7:15 4/17/2012 7:22
# 4:       1   1 4/17/2012 7:15 4/17/2012 7:45
# 5:       1   1 4/17/2012 7:15 4/17/2012 8:13
# 6:       1   2 4/17/2012 7:15 4/18/2012 6:50