[R] merging and obtaining the nearest value

[Rui Barradas]

Hello,

Try the following.


A <- read.table(text="
TYPE   DATE
A            2
A            5
A            20
B            10
B            2
", header = TRUE)


B <- read.table(text="
TYPE  Special_Date
A              2
A              6
A              20
A              22
B              5
B              6
", header = TRUE)

result <- do.call( rbind, lapply(split(merge(A, B), list(m$DATE, 
m$TYPE)), function(x){
         a <- abs(x$DATE - x$Special_Date)
         if(nrow(x)) x[which(min(a) == a), ] }) )
result$Difference <- result$DATE - result$Special_Date
result$Special_Date <- NULL
rownames(result) <- seq_len(nrow(result))
result


Also, it's a good practice to post data examples using dput(). For instance,

dput(A)
structure(list(TYPE = structure(c(1L, 1L, 1L, 2L, 2L), .Label = c("A",
"B"), class = "factor"), DATE = c(2L, 5L, 20L, 10L, 2L)), .Names = 
c("TYPE",
"DATE"), class = "data.frame", row.names = c(NA, -5L))

Now all we have to do is run the statement A <- structure(... etc...) to 
have an exact copy of the data example.
Anyway, your example with input and the wanted result was very welcome.

Hope this helps,

Rui Barradas

Em 19-08-2012 11:10, Francesco escreveu:
> Dear R-help
>
> Î would like to know if there is a short solution in R for this
> merging problem...
>
> Let say I have a dataset A as:
>
> TYPE   DATE
> A            2
> A            5
> A            20
> B            10
> B            2
>
> (there can be duplicates for the same type and date)
>
> and I have another dataset B as :
>
> TYPE  Special_Date
> A              2
> A              6
> A              20
> A              22
> B              5
> B              6
>
> The question is : I would like to obtain the difference between the
> date of each observation in A and the closest special date in B with
> the same type. In case of ties I would take the latest date of the
> two.
>
> For example I would obtain here
>
> TYPE   DATE   Difference
> A            2            0=2-2
> A            5            -1=5-6
> A            20            0=20-20
> B            10           +4=10-6
> B            2             -3=2-5
>
> Do you know how to (simply?) obtain this in R?
>
> Many thanks!
> Best Regards
>
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