From: Philippe Grosjean <phgrosjean_at_sciviews.org>

Date: Fri 27 Jan 2006 - 22:14:25 EST

# ... as many function as powers you need

}

( ( ( ( ( Prof. Philippe Grosjean

) ) ) ) )

( ( ( ( ( Numerical Ecology of Aquatic Systems ) ) ) ) ) Mons-Hainaut University, Pentagone (3D08) ( ( ( ( (

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jan 27 23:04:14 2006

Date: Fri 27 Jan 2006 - 22:14:25 EST

Hello,

Here is what I got after playing a little bit with your problem:

# First of all, if you prefer 'ln' instead of 'log', why not to define:

ln <- function(x) log(x)

ln2 <- function(x) log(x)^2 ln3 <- function(x) log(x)^3 ln4 <- function(x) log(x)^4

# ... as many function as powers you need

# Then, your formula is now closer to what you want

# which makes the whole code easier to read for you:

Form <- ln(D) ~ ln(N) + ln2(N) + ln(t) # Same as your original formula

# Here is the function to transform it in a more readable string:

formulaTransform <-

function(form, as.expression = FALSE) {

if (!inherits(form, "formula")) stop("'form' must be a 'formula' object!") # Transform the formula into a string (is it a better way?) Res <- paste(as.character(form)[c(2, 1, 3)], collapse = " ") if (as.expression) { # Transform the formula in a nice expression # Change '~' into '==' Res <- sub("~", "%~~%", Res) # How to do '~' in an expression? # Eliminate brackets Res <- gsub("[(]([A-Za-z0-9._]*)[)]", " ~ \\1", Res) # Transform powers Res <- gsub("ln([2-9])", "ln^\\1", Res) Res <- eval(parse(text = Res)) } else { # Make a nicer string # Eliminate brackets Res <- gsub("[(]([A-Za-z0-9._]*)[)]", " \\1", Res) # Transform powers Res <- gsub("ln([2-9])", "ln^\\1", Res) } # Return the result return(Res)

}

# Here is a nicer presentation as a string

formulaTransform(Form)

# Here is an even nicer presentation (creating an expression)

plot(1:3, type = "n")

text(2, 2, formulaTransform(Form, TRUE))

# The later form is really interesting when you use, for instance,

# greek letters for variables, or so...

Form2 <- ln(alpha) ~ ln(beta) + ln2(beta) + ln3(beta)

formulaTransform(Form2)

plot(1:3, type = "n")

text(2, 2, formulaTransform(Form2, TRUE))

# ... but this could be refined even more!

Best,

Philippe Grosjean

..............................................<°}))><........) ) ) ) )

( ( ( ( ( Prof. Philippe Grosjean

) ) ) ) )

( ( ( ( ( Numerical Ecology of Aquatic Systems ) ) ) ) ) Mons-Hainaut University, Pentagone (3D08) ( ( ( ( (

..............................................................

Christian Hoffmann wrote:

> Hi, > > I am trying to use sub, regexpr on expressions like > > log(D) ~ log(N)+I(log(N)^2)+log(t) > > being a model specification. > > The aim is to produce: > > "ln D ~ ln N + ln^2 N + ln t" > > The variable names N, t may change, the number of terms too. > > I succeded only partially, help on regular expressions is hard to > understand for me, examples on my case are rare. The help page on R-help > for grep etc. and "regular expressions" > > What I am doing: > > (f <- log(D) ~ log(N)+I(log(N)^2)+log(t)) > (ft <- sub("","",f)) # creates string with parts of formula, how to do > it simpler? > (fu <- paste(ft[c(2,1,3)],collapse=" ")) # converts to one string > > Then I want to use \1 for backreferences something like > > (fv <- sub("log( [:alpha:] N )^ [:alpha:)","ln \\1^\\2",fu)) > > to change "log(g)^7" to "ln^7 g", > > and to eliminate I(): sub("I(blabla)","\\1",fv) # I(xxx) -> xxx > > The special characters are making trouble, sub acceps "(", ")" only in > pairs. Code for experimentation: > > trysub <- function(s,t,e) { > ii<-0; for (i1 in c(TRUE,FALSE)) for (i2 in c(TRUE,FALSE)) for (i3 in > c(TRUE,FALSE)) for (i4 in c(TRUE,FALSE)) > print(paste(ii<-ii+1,ifelse(i1," "," ~"),"ext",ifelse(i2," "," > ~"),"perl",ifelse(i3," "," ~"),"fixed ",ifelse(i4," "," ~"),"useBytes: > ", try(sub(s,t,e, extended=i1, perl=i2, fixed=i3, > useBytes=i4)),sep=""));invisible(0) } > > trysub("I(log(N)^2)","ln n^2",fu) # A: desired result for cases > 5,6,13..16, the rest unsubstituted > > trysub("log(","ln ",fu) # B: no substitutions; errors for > cases 1..4,7.. 12 # typical errors: > "3 ext perl ~fixed useBytes: Error in sub.perl(pattern, replacement, > x, ignore.case, useBytes) : \n\tinvalid regular expression 'log('\n" > > trysub("log\(","ln ",fu) # C: same as A > > trysub("log\\(","ln ",fu) # D: no substitutions; errors for > cases 15,16 # typical errors: > "15 ~ext ~perl ~fixed useBytes: Error in sub(pattern, replacement, x, > ignore.case, extended, fixed, useBytes) : \n\tinvalid regular expression > 'log\\('\n" > > trysub("log\\(([:alpha:]+)\\)","ln \1",fu) # no substitutions, no errors > # E: typical errors: > "3 ext perl ~fixed useBytes: Error in sub.perl(pattern, replacement, > x, ignore.case, useBytes) : \n\tinvalid regular expression > 'log\\(([:alpha:]+)\\)'\n" > > > > Thanks for help > Christian > > PS. The explanations in the documents ______________________________________________R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jan 27 23:04:14 2006

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