On 07.10.2011 15:34, jdanielnd wrote:
Hello,
I am having some problems to use the 'merge' function. I'm not sure if I got
its working right.
What I want to do is:
1) Suppose I have a dataframe like:
height width
1 1.1 2.3
2 2.1 2.5
3 1.8 1.9
4 1.6 2.1
5 1.8 2.4
2) And I generate a second dataframe sampled from this one, like:
height width
1 1.1 2.3
3 1.8 1.9
5 1.8 2.4
3) Next, I add a new variable from this dataframe:
height width color
1 1.1 2.3 red
3 1.8 1.9 red
5 1.8 2.4 blue
4) So, I want to merge those dataframes, so that the new variable, color, is
binded to the first dataframe. Of course some cases won't have value for it,
since I generated this variable in a smaller dataframe. In those cases I
want the value to be NA. The result dataframe should be:
height width color
1 1.1 2.3 red
2 2.1 2.5 NA
3 1.8 1.9 red
4 1.6 2.1 NA
5 1.8 2.4 blue
I have written some codes, but they're not working properly. The new
variable has its values mixed up, and they do not correspond to its
row.names.
# Generate the first dataframe
data1<- data.frame(height=rnorm(20,3,0.2),width=rnorm(20,2,0.5))
# Sample a smaller dataframe from data1
data2<- data1[sample(1:20,15,replace=F),]
# Generate the new variable
color<- sample(c("red","blue"),15,replace=T)
# Bind the new variable to data2
data2<- cbind(data2, color)
# Merge the data1 and data2$color by row.names, and force it to has the same
values that data1. Next it generates a new dataframe where column 1 is the
row.name, and then sort it by the row.name from data1.
data.frame(merge(data1,data2$color, by=0,
all.x=T),row.names=1)[row.names(data1),]
I'm not sure what am I doing wrong. Can anyone see where the mistake is?
Just let merge do the work and prepend the rownames:
cbind(names = rownames(data1), merge(data1, data2, all.x = TRUE,
sort=FALSE))
Uwe Ligges
Thank you!
Cheers,
Joao D.
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