[R] understanding with

[Sarah Goslee]

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 at 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
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-- 
Sarah Goslee
http://www.functionaldiversity.org