r - Backreferences evaluation time in gsub -


i trying generate functions combining n gaussians, , using values retrieved nls run. use gsub replace original coefficients nls ones using backreferences. however, seems [ on datafame evaluates before \\1.

here mwe :

nls <- data.frame(estimate = seq(1,3)) row.names(nls) <- c("a","b","c") gsub("(a|b|c)",paste0(" ",nls["\\1","estimate"]," "),"a + b*x + c*x^2")

as can see, replacements nas, while call nls dataframe appear valid :

gsub("(a|b|c)",paste0(" ","\\1","estimate"," "),"a + b*x + c*x^2")

any ideas delay evaluation of [ ?

thanks !

edit : sake of clarity, here full function working great (it takes number of peaks, formula of 1 peak, parameters in formula, variable, constant boolean, , nls results arguments, , returns formula use in ggplot's stat_function() :

generate_func <- function(peaknb,peakform,peakparams, peakvar, constbool,nls){   res <- as.data.frame(summary(nls)$coefficients, optional = t)   rhs <- strsplit(peakform, "~")[[1]][[2]]   regex <- paste0("([*+-/\\^\\(\\)[:space:]]|^)(",paste0(peakparams, collapse = "|"),")([*+-/\\^\\(\\)[:space:]]|$)")   exp_names <- paste0(sapply(seq(1,peaknb),function(i){     paste0(sapply(peakparams, function(j){       paste0(j,i)     }))   }))   if(constbool){exp_names <- c("c", exp_names)}   func_text <- paste0(sapply(seq(1,peaknb),function(n){gsubfn(regex, x + y + z ~ paste0(x,res[paste0(y,n),"estimate"],z), rhs )}), collapse = " + ")   func_text <- paste0(ifelse(constbool,paste0(res["c","estimate"]," + "),""), func_text)    func <- function(x){     eval(parse(text = func_text))   }   names(formals(func)) <- c(peakvar)    print(func_text)    func }

and here usage example (nls data not included length sake):

> testfunc <- generate_func(3, "intensity_cnt ~ * exp((-(energy_ev-b)^2)/(2*c^2))", c("a","b","c"), "energy_ev", constbool = t, testnls) [1] "1000 +  32327.6598743022 * exp((-(energy_ev-1.44676439236578)^2)/(2*0.0349194350021539^2)) +  10000 * exp((-(energy_ev-1.49449385009962)^2)/(2*0.0102269096492807^2)) +  54941.8293572164 * exp((-(energy_ev-1.5321664735001)^2)/(2*0.01763494864617^2))"

thank !

1) gsub replaces pattern constant looking replace result of applying function matched string. gusbfn in gsubfn package that. below, formula in second argument gsubfn's short form function argument left hand side , body right hand side. alternately second argument expressed in usual function notation ( function(x) nls[x,] ) @ expense of bit of verbosity:

> library(gsubfn) > gsubfn("a|b|c", x ~ nls[x, ], "a + b*x + c*x^2") [1] "1 + 2*x + 3*x^2"

note "a|b|c" derived nls using paste(rownames(nls), collapse = "|") in order avoid redundant specification.

2) although gsubfn simplifies significantly, without gsubfn use substitute :

> l <- as.list(setnames(nls[[1]], rownames(nls)))  # l <- list(a = 1l, b = 2l, c = 3l) > e <- parse(text = "a + b * x + c * x ^ 2")[[1]]  # e text "call" object > s <- do.call(substitute, list(e, l))             # perform substitution > format(s)                                        # convert character [1] "1l + 2l * x + 3l * x^2"

the ls due fact nls defined in question contains integers. convert them numeric before running above if don't that:

nls[[1]] <- as.numeric(nls[[1]])

3) possibility loop on strings substituted. 

> s <- "a + b*x + c*x^2" > for(nm in rownames(nls)) s <- gsub(nm, nls[nm, ], s) > s [1] "1 + 2*x + 3*x^2"

if knew there no more 1 occurrence of each replaced use sub in place of gsub here.

update: corrected second solution.

update 2: added third solution.


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