[R] Substring replacement in string

[William Dunlap]

  string <- "pmin(1, x)"
  expr <- parse(text=string)[[1]]

will convert the string to an unevaluated language object.

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Fri, Feb 27, 2015 at 11:25 PM, Alrik Thiem <alrik.thiem at gmail.com> wrote:

> Many thanks. Unfortunately, I cannot work directly on these expressions
> since they’re only created from other strings. Would I first have to
> transform these strings to unevaluated expressions?
>
>
>
> *Von:* William Dunlap [mailto:wdunlap at tibco.com]
> *Gesendet**:* Freitag, 27. Februar 2015 23:39
> *An:* Alrik Thiem
> *Cc:* r-help at r-project.org
> *Betreff:* Re: [R] Substring replacement in string
>
>
>
> If your string will always represent an R expression, you could work with
>
> the expression directly with functions like all.names() and substitute().
>
>
>
> f <- function (expr)
>
> {
>
>     toReplace <- setdiff(all.names(expr), c("pmin", "pmax"))
>
>     toReplace <- grep(value = TRUE, "[a-z]", toReplace)
>
>     names(toReplace) <- toReplace
>
>     replacementList <- lapply(toReplace, function(name) call("-",
>
>         1, as.name(toupper(name))))
>
>     do.call(substitute, list(expr, replacementList))
>
> }
>
>
>
> > In <- quote(pmin(pmax(pmin(x1, X2), pmin(X3, X4)) == Y, pmax(Z1, z1)))
>
> > Desired <- quote(pmin(pmax(pmin(1 - X1, X2), pmin(X3, X4)) == Y,
> pmax(Z1, 1 - Z1)))
>
> > all.equal(Desired, f(In))
>
> [1] TRUE
>
>
>
>
>
>
>
>
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
>
>
> On Fri, Feb 27, 2015 at 2:19 PM, Alrik Thiem <alrik.thiem at gmail.com>
> wrote:
>
> Dear R-help list,
>
> I would like to replace all lower-case letters in a string that are not
> part
> of certain fixed expressions. For example, I have the string:
>
> "pmin(pmax(pmin(x1, X2), pmin(X3, X4)) == Y, pmax(Z1, z1))"
>
> Where I would like to replace all lower-case letters that do not belong to
> the functions "pmin" and "pmax" by 1 - toupper(...) to get
>
> "pmin(pmax(pmin(1 - X1, X2), pmin(X3, X4)) == Y, pmax(Z1, 1 - Z1))"
>
> Any ideas on how I could achieve that?
>
> Many thanks and best wishes,
>
> Alrik
>
>
> ********************************
> Alrik Thiem
> Post-Doctoral Researcher
>
> Department of Philosophy
> University of Geneva
> Rue de Candolle 2
> CH-1211 Geneva
>
> +41 76 527 80 83
>
> http://www.alrik-thiem.net
> http://www.compasss.org
>
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