Like others on the list I have no interest in wading through your
block of HTML-mangled text.
But if your question is clearly stated by the subject line, then it's
quite straightforward.
with() saves you typing and often increases code clarity by telling R
where to look for named variables
# This example is best done in a clean R session
# Given some R objects
myLongDataframeName <- data.frame(x = runif(10), y = runif(10))
x <- 1:10
y <- 1:10
cor(myLongDataframeName$x, myLongDataframeName$y) # uses the data
frame columns named x and y
cor(x, y) # uses the R objects named x and y
# Here's the magic of with():
with(myLongDataframeName, cor(x, y)) # uses the data frame columns named x and y
On Fri, Sep 9, 2016 at 12:46 AM, Carl Sutton via R-help
<r-help@r-project.org> wrote:
> Hi I have been doing theR-exercises to improve my R programming
> capabilities. Data.frame exercise4 showed me that I have a languageproblem.
> Yes, I am frustrated, but please don’t take this as acriticism of the R
> language. Theroutines I have managed to write do marvelous things in a short
> period oftime. I really want to do more, but thisis a steep rocky thick with
> underbrush hill that is not fun to climb. But there are good resources.
> Swirl is wonderful. My thanks to the authors of thatpackage. Jared Lander’s
> R for Everyoneis a really good beginners book. DataCamp, Coursera, all
> informative courses. Yes I’m frustrated. After a couple of years on and off
> takingclasses, reading books, reading stack overflow and r-help just about
> daily, Iam learning to almost crawl. At one timeI thought I had advanced to
> walking but days like today show me I’m a toddlerabout to fall on his
> backside. Reading the manuals onCRAN is analogous to reading the tax code.
> Without a specific objective for motivation, reading them is either painfulor
> a certain cure for insomnia. Here's the problem Ireferred to at the beginning
> and my "solution". # Exercise 4 fromR Exercises# Create a simpledata frame
> from 3 vectors. Order the entire data frame by the# first column.df2 <-
> data.frame(a =5:1,b = letters[1:5], c = runif(5))order(df2$a) Naturally the
> orderfunction did nothing. But I did read the help page and thought I
> followedit. And there is no obvious environmentissue. It’s a simple
> data.frame and Iwant to order it by one column. Such asdf2 <-
> data.table(df2)setkey(df2, a). Done. No fuss, no muss, no needing “with”.
> Per "help"Description order returns apermutation which rearranges its first
> argument into ascending or descendingorder, breaking ties by further
> arguments. sort.list is the same, using onlyone argument.See the examples for
> howto use these functions to sort data frames, etc. Usage order(..., na.last
> =TRUE, decreasing = FALSE, method = c("shell", "radix")) sort.list(x,
> partial =NULL, na.last = TRUE, decreasing = FALSE, method =
> c("shell", "quick","radix"))Arguments ... a sequence of numeric,complex,
> character or logical vectors, all of the same length, or a classed Robject.
> Well, doesn't ... meanany legal object? I gave it a legal object and got
> nada. And the answerabsolutely has me screaming "Say
> What"df2[with(df2,order(a)),] What's with "with? In Mr. Lander’s book, page
> 126, “Here we used a new function, with. This allows us to specify the
> columns of adata frame without having to specify the data.frame name each
> time.” Great, I’m a horrible typist and will takeany and all typing
> shortcuts. However, Idon’t use it because I don’t understand what it does.
> Obviously it’s important, but I’m stuck on why or how I would use it. It is
> one function I donot use because I find it incomprehensible. To witEvaluate
> an R expressionin an environment constructed from data, possibly modifying (a
> copy of) theoriginal data. First of all, if I'm notmodifying data (or as a
> subset activity creating data), why am I doing whateverit is I'm doing?
> ("possibly modifying (a copy of) the originaldata.") Possibly?? Evaluate.
> According to the thesaurus a) assess(v), b) appraise, c) gage. OK, am I in a
> safe area? I'll evaluate that. Do I desire future social contact with
> thisperson? I'll evaluate that. In no way do I ever evaluatean equation. I
> may attempt to solve it. I may do a computer programto do the calculations
> and return a result. I will probably evaluate theresult as to whether or not
> it helps solve the problem. Think in terms ofan income tax return. But
> evaluate an R expression? No clue whatthat might mean. And that is my
> problemin a nutshell. The remainder of thedefinition is also obtuse. an R
> expression in an environmentconstructed from data. Why would one make an
> environment withoutdata? Obviously I am missing thepoint. My own created
> function makes a new environment, but I onlycreated it to crunch numbers. If
> it doesn't crunch numbers it's useless. The point is, I do not understand the
> definitionof "with" and thus have no idea how to use it. I guesscomputerese
> is analogous to taxlawese. Familiar words have entirely different meanings.
> Carl Sutton CPA
>
> [[alternative HTML version deleted]]
--
Sarah Goslee
http://www.functionaldiversity.org
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