[R] accessing variables inside a function, inside a loop

[Joshua Wiley]

Dear Sacha,

That is the most piteous soliloquy I have read in some time.  Here
then a response to soothe your dizzied mind and wrest your rest from
the ornery sprites that so threaten to plague it now.

## Some sample data
water <- as.data.frame(matrix(rnorm(120), ncol = 12))
## Adding your names
names(water) <- c("site", "sample", "temp", "pH", "DO", "BOD",
  "COD", "no3", "no2", "po4", "N_male", "N_female")

par(mfrow = c(4, 2))

## Simplest
lapply(water[, 3:10], FUN = plot, y = water[, "N_male"])

## Slightly fancier
plotter <- function(x) {
  form <- eval(substitute(N_male ~ p, list(p = as.name(x))))
  plot(form, data = water)
}

##
lapply(names(water[, 3:10]), plotter)

## Or if you wanted to start getting "really" fancy
## you could wrap it all up

jwrap <- function(y, x, dat, mfrow) {
  old.par <- par(no.readonly = TRUE)
  on.exit(old.par)
  par(ask = TRUE, mfrow = mfrow)

  jplot <- function(x, y) {
    form <- eval(substitute(y ~ p, list(y = as.name(y), p = as.name(x))))
    plot(form, data = water)
  }

  lapply(X = names(dat[, x]), FUN = jplot, y = y)
}

## jwrap() in action
jwrap("N_male", x = 3:10, dat = water, mfrow = c(4, 2))
## and showing what happens if you change mfrow
jwrap("N_male", x = 3:10, dat = water, mfrow = c(2, 2))

In all good cheer,

Joshua

On Sun, Feb 27, 2011 at 12:48 PM, Sacha Viquerat <tweedie-d at web.de> wrote:
> dear list!
> I KNOW this has been answered a million times before. But, as some might
> remember from their "freelance" times as a statistic consultant, sometimes
> you're blinded by the facts. I KNOW I have seen this problem solved, but due
> to the mental blockade i have been suffering from the last 3 hours, I can
> neither find the answer on the mailing list nor on google. I wrote a
> function to plot one continuous variable against an abundance of fish, the
> data is called water. however, my data covers 9 parameters, and since I am
> lazy as hell, I decided to write a for loop to pass all the variables to the
> function. as usual, the variables and the data frame cannot be found inside
> the function.
>
> water<-read.csv("Henni/water-abundance2.csv",sep="\t",header=T)
> source("functions.R")
> attach(water)
>
> names(water):
>  [1] "site"     "sample"   "temp"     "pH"       "DO"       "BOD"
>  [7] "COD"      "no3"      "no2"      "po4"      "N_male"   "N_female"
>
> vars<-names(water)[3:10]
>
> par(mfrow=c(4,2))
> for (i in vars)
> {
>    comp.plot(i,N_male,DATA=water)
> }
>
> comp.plot<-function(parameter,y,DATA){ #this is actually in functions.R
>    x<-DATA[[parameter]]
>    y<-DATA[[y]]
>    plot(y~parameter)
> }
>
> and of course, this doesn't work. I am really frustrated by now, since I
> have gathered all I could recollect from my past 2 years of R experience but
> still, I was not able to find a solution. I'm really dizzy right now, but
> since I will not be able to go to sleep unless I have found the answer to
> this problem, I urge someone to shed some light on my trivial problem! I
> will promise not to post this question ever again, but for now, I'm just
> stuck!
>
> Thanks in advance and humble apologies to all that feel offended by my post!
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/