合并数据帧并覆盖值 [英] Merge data frames and overwrite values

问题描述

如何合并2个相似的数据框，但其中一个具有更高的重要性?

How do I merge 2 similar data frames but have one with greater importance?

例如:

数据框1

Date      Col1    Col2
jan         2      1
feb         4      2
march       6      3
april       8      NA

数据框2

Date      Col2    Col3
jan         9      10
feb         8      20
march       7      30
april       6      40

按日期将其合并，数据框1优先，数据框2填充空白

merge these by Date with dataframe 1 taking precedence but dataframe 2 filling blanks

DataframeMerge

DataframeMerge

Date      Col1    Col2    Col3
jan         2       1      10
feb         4       2      20
march       6       3      30
april       8       6      40

编辑-解决方案

commonNames <- names(df1)[which(colnames(df1) %in% colnames(df2))]
commonNames <- commonNames[commonNames != "key"]
dfmerge<- merge(df1,df2,by="key",all=T)
for(i in commonNames){
  left <- paste(i, ".x", sep="")
  right <- paste(i, ".y", sep="")
  dfmerge[is.na(dfmerge[left]),left] <- dfmerge[is.na(dfmerge[left]),right]
  dfmerge[right]<- NULL
  colnames(dfmerge)[colnames(dfmerge) == left] <- i
}

推荐答案

merdat <- merge(dfrm1,dfrm2, by="Date")  # seems self-documenting

#  explanation for next line in text below.
merdat$Col2.y[ is.na(merdat$Col2.y) ] <- merdat$Col2.x[ is.na(merdat$Col2.y) ]

然后只需将'merdat $ Col2.y'重命名为'merdat $ Col2'并删除'merdat $ Col2.x'.

Then just rename 'merdat$Col2.y' to 'merdat$Col2' and drop 'merdat$Col2.x'.

作为对更多评论的要求的回复:仅更新向量部分的一种方法是构造一个逻辑向量以进行索引，并使用"["将其应用于赋值的两面.另一种方法是设计一个逻辑矢量，该逻辑矢量仅位于分配的LHS上，然后使用与sum(logical.vector)相同长度的rep()来创建矢量.目标是两个实例都具有与要替换的物品相同的长度(和顺序).

In reply to request for more comments: One way to update only sections of a vector is to construct a logical vector for indexing and apply it using "[" to both sides of an assignment. Another way is to devise a logical vector that is only on the LHS of an assignment but then make a vector using rep() that has the same length as sum(logical.vector). The goal is both instances is to have the same length (and order) for assignment as the items being replaced.

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