CODEWITHSUNDEEP
rdataframeappend
DeltaIV
DeltaIV

Reputation: 5646

Most efficient to append some columns of a data frame to some other columns

Suppose I have the following data frame:

foo <- data.frame(a=letters,b=seq(1,26),
                  n1=rnorm(26),n2=rnorm(26),
                  u1=runif(26),u2=runif(26))

I want to append columns u1 and u2 to columns n1 and n2. For now, I found the following way:

df1 <- foo[,c("a","b","n1","n2")]
df2 <- foo[,c("a","b","u1","u2")]
names(df2) <- names(df1)
bar <- rbind(df1,df2)

That does the trick. However, it seems a little bit involved. Am I too picky? Or is there a faster/simpler way to do this in R?

Upvotes: 1

Views: 66

Answers (3)

Martin Morgan
Martin Morgan

Reputation: 46856

Use Map() to concatenate the columns, and cbind() with recycling to arrive at the final data frame.

cbind(foo[1:2], Map(c, foo[3:4], foo[5:6]))

Substitute numerical indexes with column names, if desired.

cbind(foo[c("a", "b")], Map(c, foo[c("n1", "n2")], foo[c("u1", "u2")]))

Upvotes: 2

JasonAizkalns
JasonAizkalns

Reputation: 20463

Short-hand:

rbind(foo[1:4], setNames(foo[c(1, 2, 5, 6)], names(foo[1:4])))

Long-winded:

rbind(foo[c("a", "b", "n1", "n2")], setNames(foo[c("a", "b", "u1", "u2")], c("a", "b", "n1", "n2")))

Long-winded (more DRY):

nms <- c("a", "b", "n1", "n2")
rbind(foo[nms], setNames(foo[c("a", "b", "u1", "u2")], nms))

Upvotes: 1

Steven Beaupr&#233;
Steven Beaupr&#233;

Reputation: 21621

Here is one way using full_join() from dplyr:

library(dplyr)
full_join(df1, df2, by = c("a", "b", "n1" = "u1", "n2" = "u2"))

From the documentation:

full_join

return all rows and all columns from both x and y. Where there are not matching values, returns NA for the one missing.

by

a character vector of variables to join by. If NULL, the default, join will do a natural join, using all variables with common names across the two tables. A message lists the variables so that you can check they're right.

To join by different variables on x and y use a named vector. For example, by = c("a" = "b") will match x.a to y.b.

Upvotes: 3

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