[R] joining "one-to-many"
Monica Pisica
pisicandru at hotmail.com
Tue Feb 17 16:28:43 CET 2009
Ok,
I feel properly ashamed. I suppose my "real" data is a little bit different than my toy data (although i don't know how) because i did try the merge function as simple as merge(t1, t2) and did not work. Maybe a reset of my session will solve my problems and more coffee my confusion.
Again, thanks for your help,
Monica
----------------------------------------
> Date: Tue, 17 Feb 2009 10:09:17 -0500
> Subject: Re: [R] joining "one-to-many"
> From: ggrothendieck at gmail.com
> To: pisicandru at hotmail.com
> CC: r-help at r-project.org
>
> Try merge(t1, t2)
>
>
> On Tue, Feb 17, 2009 at 9:33 AM, Monica Pisica wrote:
>>
>> Hello list,
>>
>> I am wondering if a joining "one-to-many" can be done a little bit easier. I tried merge function but I was not able to do it, so I end up using for and if.
>>
>> Suppose you have a table with locations, each location repeated several times, and some attributes at that location. The second table has the same locations, but only once with a different set of attributes. I would like to add the second set of attributes to the first table.
>>
>> Example:
>>
>> set.seed <- 123
>> loc <- c(rep("L1", 3), rep("L2", 5), rep("L3", 2))
>> val1 <- round(rnorm(10),2)
>> val2 <- c("a", "b", "c", "a", "b", "d", "f", "e", "b", "e")
>> t1 <- data.frame(loc, val1, val2)
>> t2 <- data.frame(loc=c("L1","L2","L3"), val3 = c("m", "n", "p"), val4 = c(25, 67, 48))
>>
>> # join one-to-many
>>
>> n <- nrow(t1)
>> m <- nrow(t2)
>> t1$val3 <- rep(1, n)
>> t1$val4 <- rep(1, n)
>>
>> for (i in 1:n) {
>> for (j in 1:m){
>> if (t1$loc[i]==t2$loc[j]) {
>> t1$val3[i] <- as.character(t2$val3[j])
>> t1$val4[i] <- t2$val4[j]
>> }
>> }
>> }
>>
>> Desired result:
>>
>> t1
>> loc val1 val2 val3 val4
>> 1 L1 -0.41 a m 25
>> 2 L1 -0.69 b m 25
>> 3 L1 0.36 c m 25
>> 4 L2 1.11 a n 67
>> 5 L2 0.15 b n 67
>> 6 L2 -0.80 d n 67
>> 7 L2 -0.08 f n 67
>> 8 L2 -1.01 e n 67
>> 9 L3 -1.01 b p 48
>> 10 L3 -2.50 e p 48
>>
>>
>> This code works OK but it is slow if the data frames are actually bigger than my little example. I hope somebody knows of a better way of doing these type of things.
>>
>> Thanks,
>>
>> Monica
>> _________________________________________________________________
>>
>>
>> 22009
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
More information about the R-help
mailing list