[R] Find all numbers in a certain interval

[Antje]

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 ), ]

instead of:

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

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
> 
> 
>