[R] function to filter identical data.fames using less than (<) and greater than (>)

[Karl Brand]

Rui,

Indeed it does help. Also very happy to see eval() and parse() employed 
and demystified here.

In Rdulation,

Karl

On 06/12/12 15:48, Rui Barradas wrote:
> Hello,
>
> Something like this?
>
>
> func <- function(data, A, B, C){
>      f <- function(a)
>          function(x) eval(parse(text = paste("x", a)))
>      iA <- if(is.na(A)) TRUE else f(A)(data$A)
>      iB <- if(is.na(B)) TRUE else f(B)(data$B)
>      iC <- if(is.na(C)) TRUE else f(C)(data$C)
>      data[iA & iB & iC, ]
> }
>
> func(eg, "> 0", NA, NA)
> func(data=eg, A="< 0", B="< 1", C="> 0")
>
>
> Hope this helps,
>
> Rui Barradas
> Em 06-12-2012 13:49, Karl Brand escreveu:
>> Esteemed UseRs,
>>
>> I've got many biggish data frames which need a lot subsetting, like in
>> this example:
>>
>> # example
>> eg <- data.frame(A = rnorm(10), B = rnorm(10), C = rnorm(10), D =
>> rnorm(10))
>> egsub <- eg[eg$A < 0 & eg$B < 1 & eg$C > 0, ]
>> egsub
>> egsub2 <- eg[eg$A > 1 & eg$B > 0, ]
>> egsub2
>>
>> # To make this clearer than 1000s of lines of extractions with []
>> # I tried to make a function like this:
>>
>> # func(data="eg", A="< 0", B="< 1", C="> 0")
>>
>> # Which would also need to be run as
>>
>> # func(data="eg", A="> 1", B="> 0", C=NA)
>> #end
>>
>> Noteably:
>> -the signs* "<" and ">" need to be flexible _and_ optional
>> -the quantities also need to be flexible
>> -column header names i.e, A, B and C don't need flexibility,
>> i.e., can remain fixed
>> * "less than" and "greater than" so google picks up this thread
>>
>> Once again i find just how limited my grasp of R is...Is do.call() the
>> best way to call binary operators like < & > in a function? Is an
>> ifelse statement needed for each column to make filtering on it
>> optional? etc....
>>
>> Any one with the patience to show their working version of such a
>> funciton would receive my undying Rdulation. With thanks in advance,
>>
>> Karl
>>
>

-- 
Karl Brand
Dept of Cardiology and Dept of Bioinformatics
Erasmus MC
Dr Molewaterplein 50
3015 GE Rotterdam
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