我有两个共享相同因素的数据框，但不要重复相同次数的级别。我需要根据因子级别将第二个数据框中的变量值导入第一个数据框。以下是两个数据框的示例：
First DF：
User Issue Logged Other.Variable Other.Variable Quartile
A File Download
A Log-In
A File Download
B File Upload
C File Upload
C File Upload
D Log-In
D File Download
D File Upload
D Log-In
第二次DF：
User Issue.Frequency Quartile
A 3 3
B 1 1
C 2 2
D 4 4
我想将第二个DF中的Quartile值放入第一个DF，这样我就可以根据四分位数对第一个DF进行子集化。我尝试使用ifelse语句：
DF1$Quartile <- ifelse (DF1$User %in% DF2$User, DF2$Quartile, "Failed")
但这只是重复了DF2四分位数值，而没有将它们与相关用户实际匹配：
First DF：
User Issue Logged Other.Variable Other.Variable Quartile
A File Download 3
A Log-In 1
A File Download 2
B File Upload 4
C File Upload 3
C File Upload 1
D Log-In 2
D File Download 4
D File Upload 3
D Log-In 1
当我想要的是：
First DF：
User Issue.Logged Other.Variable Other.Variable Quartile
A File Download 3
A Log-In 3
A File Download 3
B File Upload 1
C File Upload 2
C File Upload 2
D Log-In 4
D File Download 4
D File Upload 4
D Log-In 4
我理解为什么我的第一个ifelse语句失败了（它只是为每个返回true的匹配输入Quartile变量），但我不知道如何继续，以便根据相关用户放置四分位数值（因子水平）。我还尝试了ifelse语句的其他一些变体，但遇到了错误，例如：
for (i in DF1$User %in% DF2$User) DF1$Quartile <- DF2$Quartile
Error in `$<-.data.frame`(`*tmp*`, "Quartile", value = c(1L, 1L, 1L, 1L, :
replacement has 4 rows, data has 10
有人能让我直截了当吗？或者为资源提供一些指导，帮助我解决这个问题？
提前致谢！