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I want to merge two data frames, skipping rows based on a specific column value, but still keep the skipped rows in the final merged data frame. I can manage the first part (skipping), but not the second.

Here are the data frames:

# Data frame 1 values
ids1 <- c(1:3)
x1 <- c(100, 101, 102)
doNotMerge <- c(1, 0, 0)

# Data frame 2 values
ids2 <- c(1:3)
x2 <- c(200, 201, 202)

# Creating the data frames
df1 <- as.data.frame(matrix(c(ids1, x1, doNotMerge),
                            nrow = 3,
                            ncol = 3,
                            dimnames = list(c(),c("ID", "X1", "DoNotMerge"))))

df2 <- as.data.frame(matrix(c(ids2, x2),
                            nrow = 3,
                            ncol = 2,
                            dimnames = list(c(),c("ID", "X2"))))

# df1 contents:
#   ID  X1 DoNotMerge
# 1  1 100          1
# 2  2 101          0
# 3  3 102          0

# df2 contents:
#   ID  X2
# 1  1 200
# 2  2 201
# 3  3 202

I used merge:

merged <- merge(df1[df1$DoNotMerge != 1,], df2, by = "ID", all = T)

# merged contents:
#   ID  X1 DoNotMerge  X2
# 1  1  NA         NA 200
# 2  2 101          0 201
# 3  3 102          0 202

The skipping part I was able to do, but what I actually want is to keep the df1 row where DoNotMerge == 1, like so:

#   ID  X1 DoNotMerge  X2
# 1  1  NA         NA 200
# 2  1 100          1  NA
# 3  2 101          0 201
# 4  3 102          0 202

Can anyone please help? Thanks.

David Spivak
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    Possible duplicate of [Merge data sets by row differening columns](http://stackoverflow.com/questions/7896909/merge-data-sets-by-row-differening-columns) – Hack-R May 21 '16 at 14:57

1 Answers1

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Update: I actually found the solution while writing the question (ran into this question), so figured I'd post it in case someone else encounters this problem:

require(plyr)
rbind.fill(merged, df1[df1$DoNotMerge == 1,])

# Result:
#  ID  X1 DoNotMerge  X2
# 1  1  NA         NA 200
# 2  2 101          0 201
# 3  3 102          0 202
# 4  1 100          1  NA
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David Spivak
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