complex search between dataframes

Hi!

I am very new to R, I hope someone can help me.

I have two dataframes:

data1<-data.frame(from=c(1,12,16,40,55,81,101),to=c(10,13,23,45,67,99,123))
data2<-data.frame(name=c(1,2,3,4,5,6,7,8,9),position=c(2,14,20,50,150,2000,2001,2002,85))


I want to know which of the entries in "position" of data2 are included between 
any "from" and the corresponding "to" of data1.

So in this case I would need to somehow be able to extract 2,20 and 85, 
corrisponding to the "name"s 1,3 and 9.

Thank you very much!
Filippo

See ?findInterval

Coerce data1 into a matrix, so that the interval boundaries are in increasing order by columns, which is then actually used by findInterval as a vector (eg. c(1, 10, 12, ...)):

t(data1)

[,1] [,2] [,3] [,4] [,5] [,6] [,7]
from    1   12   16   40   55   81  101
to     10   13   23   45   67   99  123


findInterval() will return the interval indices for each data2$position value within the sorted intervals. Since your actual intervals are discontinuous, you only want the values that fit in the odd intervals, which is where the use of %in% seq(1, 13, 2) comes in. Prior to that, findInterval() returns:

findInterval(data2$position, t(data1))

[1]  1  4  5  8 14 14 14 14 11

With it:

findInterval(data2$position, t(data1)) %in% seq(1, 13, 2)

[1]  TRUE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE

Now you can use the TRUE values to index data2$name:

data2$name[findInterval(data2$position, t(data1)) %in% seq(1, 13, 2)]

[1] 1 3 9

or data2$position:

data2$position[findInterval(data2$position, t(data1)) %in% seq(1, 13, 2)]

[1]  2 20 85



HTH,

Marc Schwartz