# [R] Find all numbers in a certain interval

David Winsemius dwinsemius at comcast.net
Tue Dec 16 13:41:26 CET 2008

```On Dec 16, 2008, at 7:19 AM, Antje wrote:

> Hi David,
>
> thanks a lot for your proposal. I got a lot of useful hints from all
> of you :-)
>
> David Winsemius schrieb:
>> It's not entirely clear what you are asking for, since
>> which(within.interval(a, -0.5, 0.5)) is actually longer than
>> which(a > -0.5 & a < 0.5).
>
> Right but in case 'a' is something with a long name and '0.5' is a
> variable you might end up with something like this (for the data
> frame example):
>
> DF[which( DF\$myReallyLongColumnName > -myReallyLongThreshold & DF
> \$myReallyLongColumnName < -myReallyLongThreshold ), ]

I see your point, but I must point out that no cases would ever
satisfy that construction.

>
>
>
> DF[which( within.interval(DF\$myReallyLongColumnName,
> myReallyLongThreshold), ]

That would be a different within.interval function than I suggested,
but you could certainly create one which accepted a vector.

within.interval <- function(x, y) { min(y) < x & x < max(y) }
----------
> within.interval2 <- function(x,y) { min(y) < x & x < max(y)}

> y <- c(-.1, -.2, .1,.2)

> which(within.interval2(DF\$a,y))
[1]  7 13 14 17

>
>
> You mention that you want a solution that applies to
>> dataframes. Using indexing you can get entire rows of dataframes
>> that satisfy multiple conditions on one of its columns:
>> >> DF <- data.frame(a = rnorm(20), b= LETTERS[1:20], c =
>> letters[20:1], stringsAsFactors=FALSE)
>> > DF[which( DF\$a > -0.5 & DF\$a < 0.5 ), ]
>>  # note that one needs to avoid DF[which(a > -0.5 & a<0.5) , ]
>>  # the "a" vector is not the same as the "a" column vector within DF
>>             a b c
>> 3  -0.47310672 C r
>> 6  -0.49784460 F o
>> 9   0.02571058 I l
>> 10  0.16893759 J k
>> 11 -0.11963322 K j
>> 12  0.39378887 L i
>> 16  0.03712263 P e
>> Could get the indices that satisfy more than one condition:
>> > which(DF\$a > 0.5 & DF\$b < "K")
>> [1]  1  2  6 10
>> Or you can get rows of DF that satisfy conditions on multiple
>> columns with the subset function:
>> > subset(DF, a > 0.5 & b < "K")
>>           a b c
>> 1  2.2500997 A t
>> 2  0.7251357 B s
>> 6  0.7845355 F o
>> 10 1.0685649 J k
>> Or if you wanted a within.interval function
>> > within.interval <- function(x,a,b) { x > a & x < b}
>> > which(within.interval(DF\$a, -0.5, 0.5))
>> [1]  3  4  7  8  9 13 14 17 20
>>
>
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