Hi Sarah
I see the difference, but pardon the big yawn, who writes code using the
same variable names in separate vectors and lists/data.frames? That smacks
of bad planning in variable name selection and an invitation to disaster.
If it can happen, it will. Looks to me there is a possible lack of planning
on the programmers part. List variable names start with lst, data frames
with df, data tables dt, and vectors as descriptive as possible. If any of
them are the same, I messed up.
Carl Sutton CPA
On Friday, September 9, 2016 6:39 AM, Sarah Goslee <sarah.gos...@gmail.com>
wrote:
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
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--
Sarah Goslee
http://www.functionaldiversity.org
