[R] Dynamic reference, right-hand side of function

William Dunlap
Tue, 05 Dec 2017 00:40:40 -0000

By the way, R 'vectors' are not the equivalents of mathematical
'vectors'.
In R, a vector is something that can have arbitrary length and which has
no 'attributes', other than perhaps element names.  Vectors can be
numeric,
character,
complex, lists, etc.   Functions, names, and NULL are not vectors.  In my
opinion,
the typical data scientist will rarely find the R vector concept useful and
it more
likely to make mistakes with it.

Instead of using as.vector and is.vector, use as.numeric or as.character,
etc.,
and is.numeric or is.character, naming the type you want.


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Dec 4, 2017 at 4:23 PM, Love Bohman <love.bohman at
sociology.su.se>
wrote:

> Hi again!
> I know you don't find loops evil (well, at least not diabolic :-) ).
> (After many hours googling I have realized that thinking about loops rather
> than lists is a newbie thing we Stata-users do, I just jokingly pointed it
> out). Anyway, I'm really happy that you try to teach me some R-manners.
> Since I still get questions about what the h**k I mean by my strange
> question, I sort it out with an example:
>
> I had a number of matrices, named in a consecutive manner:
>
> aa_2000 <-
as.matrix(read.csv(text="1,0,1,1,0,0,0,0,0,0,1,0,0",
> header=FALSE))
> aa_2001 <- as.matrix(read.csv(
text="0,0,0,1,0,1,1,0,0,0,0,1,0,0",
> header=FALSE))
> aa_2002 <- as.matrix(read.csv(
text="1,0,0,0,0,0,0,0,1,0,0,0,0,1,0,0",
> header=FALSE))
>
> I needed them to be vectors, and they weren't:
>
> is.vector(aa_2000)
>
> I finally solved it with this loop (well, I admit I shaped up the last
> line thanks to William Dunlap):
>
> for (year in 2000:2002){
> varname <- paste0("aa_",year)
> assign(varname, as.vector(eval(as.name(varname))))
> }
>
> The loop obviously solved the problem:
>
> is.vector(aa_2000)
>
> However, you have taught me that I should have solved it more elegant with
> a data list:
>
> bb_2000 <-
as.matrix(read.csv(text="1,0,1,1,0,0,0,0,0,0,1,0,0",
> header=FALSE))
> bb_2001 <- as.matrix(read.csv(
text="0,0,0,1,0,1,1,0,0,0,0,1,0,0",
> header=FALSE))
> bb_2002 <- as.matrix(read.csv(
text="1,0,0,0,0,0,0,0,1,0,0,0,0,1,0,0",
> header=FALSE))
>
> is.vector(bb_2000)
>
> datanames <- paste0("bb_", 2000:2002)
> datalist <- lapply(datanames, get)
> is.vector(datalist[1])
>
>
> I learned a lot of code today, and I really appreciate it! A million
> thanks!
> My R-superpowers are, well, not as minuscule as when I woke up this
> morning.
>
> All the best,
> Love (or maybe LoveR, my future superhero name)
>
>
>
> -----Ursprungligt meddelande-----
> Fr?n: Jeff Newmiller [mailto:jdnewmil at dcn.davis.ca.us]
> Skickat: den 5 december 2017 00:01
> Till: Love Bohman <love.bohman at sociology.su.se>
> Kopia: peter dalgaard <pdalgd at gmail.com>; r-help at r-project.org
> ?mne: Re: [R] Dynamic reference, right-hand side of function
>
> Loops are not evil, and no-one in this thread said they are. But I believe
> your failure to provide a reproducible example is creating confusion, since
> you may be using words that mean one thing to you and something else to the
> readers here.
>
> ################################
> # A reproducible example includes a tiny set of sample data # Since we
> cannot reproducibly refer to filenames (your directories # and files in
> them are unlikely to be like mine), I will # use a little trick to read
> from data in the example:
>
> dta <- read.csv( text> "1.1,3.0,5,7.4,4,2.2,0
> ", header=FALSE)
> str(dta)
> #> 'data.frame':    1 obs. of  7 variables:
> #>  $ V1: num 1.1
> #>  $ V2: num 3
> #>  $ V3: int 5
> #>  $ V4: num 7.4
> #>  $ V5: int 4
> #>  $ V6: num 2.2
> #>  $ V7: int 0
>
> # note that I did not use "data" as the name because # there is a
> commonly-used function by that name in R # that could be confused with your
> variable
>
> # if you have your object already in memory, you can use the # dput
> function to create R code that will re-create it in our # working
> environments.
>
> dput( dta )
> #> structure(list(V1 = 1.1, V2 = 3, V3 = 5L, V4 = 7.4, V5 = 4L,
> #>     V6 = 2.2, V7 = 0L), .Names = c("V1", "V2",
"V3", "V4", "V5",
> #> "V6", "V7"), class = "data.frame",
row.names = c(NA, -1L))
>
> # which you can put a variable name in front of in your example code:
>
> dtasample <- structure(list( V1 = 1.1, V2 = 3, V3 = 5L , V4 = 7.4, V5
> 4L, V6 = 2.2, V7 = 0L ) , .Names = c( "V1"
> , "V2", "V3", "V4", "V5",
"V6", "V7" ), class = "data.frame"
> , row.names = c(NA, -1L) )
>
> # and starting with that line you can make a self-contained #
> (reproducible) example for us to investigate your problem with
>
> # Note that reading a single row of data into R usually gets # a data
> frame, which looks like a matrix but is not a matrix.
> # Read the Introduction to R about these two types carefully.
> # Each column in a data frame can have a different type of data, # but in
> a vector or a matrix all rows and columns must be of # the same type.
>
> dtam <- as.matrix( dta )
>
> # If you have any values that R cannot clearly identify as numeric # or
> integer, then the next most general type of variable is # character... and
> that is often something that trips up newbies, # though I have no evidence
> that you have any non-numeric columns # in your data frames.
>
> dtax <- as.vector( dta )
> str(dtax)
> #> 'data.frame':    1 obs. of  7 variables:
> #>  $ V1: num 1.1
> #>  $ V2: num 3
> #>  $ V3: int 5
> #>  $ V4: num 7.4
> #>  $ V5: int 4
> #>  $ V6: num 2.2
> #>  $ V7: int 0
>
> # This actually makes no change to dta, because a data frame is already #
> a list of columns, and lists are just vectors that can hold different #
> types of variables, so dta is already a kind of vector.
>
> dtan <- as.numeric( dta )
> str(dtan)
> #>  num [1:7] 1.1 3 5 7.4 4 2.2 0
>
> # I suspect this is what you are trying to accomplish... but really, # if
> we had an example of the data you are working with, we would # already
know.
> ################################
>
> Some more explanations of reproducibility [1][2][3]
>
> [1] http://stackoverflow.com/questions/5963269/how-to-make-
> a-great-r-reproducible-example
>
> [2] http://adv-r.had.co.nz/Reproducibility.html
>
> [3] https://cran.r-project.org/web/packages/reprex/index.html (read the
> vignette)
>
>
> On Mon, 4 Dec 2017, Love Bohman wrote:
>
> > :-)
> > I don't insist on anything, I'm just struggling to learn a new
language
> and partly a new way of thinking, and I really appreciate the corrections.
> I hope I someday will be able to handle lists in R as easy as I handle
> loops in Stata...
> > Thanks again!
> >
> > Love
> >
> >
> > -----Ursprungligt meddelande-----
> > Fr?n: peter dalgaard [mailto:pdalgd at gmail.com]
> > Skickat: den 4 december 2017 23:09
> > Till: Love Bohman <love.bohman at sociology.su.se>
> > Kopia: r-help at r-project.org
> > ?mne: Re: [R] Dynamic reference, right-hand side of function
> >
> > Um, if you insist on doing it that way, at least use
> >
> > assign(varname, as.vector(get(varname)))
> >
> > -pd
> >
> >> On 4 Dec 2017, at 22:46 , Love Bohman <love.bohman at
sociology.su.se>
> wrote:
> >>
> >> Hi!
> >> Thanks for the replies!
> >> I understand people more accustomed to R doesn't like looping
much, and
> that thinking about loops is something I do since I worked with Stata a
> lot. The syntax from Peter Dalgaard was really clever, and I learned a lot
> from it, even though it didn't solve my problem (I guess it wasn't
very
> well explained). My problem was basically that I have a data matrix
> consisting of just 1 row, and I want to convert that row into a vector.
> However, when trying to do that dynamically, I couldn't get R to read
the
> right hand side of the syntax as a variable name instead of a string.
> However, together with a colleague I finally solved it with the (eval(
> as.name()) function (I include the loop I used below). I understand that
> looping isn't kosher among you more devoted R-users, and eventually I
hope
> I will learn to use lists in the future instead.
> >>
> >> Thanks!
> >> Love
> >>
> >>
> >> for (year in 2000:2007){
> >> varname <- paste0("aa_",year)
> >> assign(paste0(varname), as.vector(eval(as.name(varname))))
> >> }
> >>
> >> -----Ursprungligt meddelande-----
> >> Fr?n: peter dalgaard [mailto:pdalgd at gmail.com]
> >> Skickat: den 4 december 2017 16:39
> >> Till: Love Bohman <love.bohman at sociology.su.se>
> >> Kopia: r-help at r-project.org
> >> ?mne: Re: [R] Dynamic reference, right-hand side of function
> >>
> >> The generic rule is that R is not a macro language, so looping of
names
> of things gets awkward. It is usually easier to use compound objects like
> lists and iterate over them. E.g.
> >>
> >> datanames <- paste0("aa_", 2000:2007)
> >> datalist <- lapply(datanames, get)
> >> names(datalist) <- datanames
> >> col1 <- lapply(datalist, "[[", 1)
> >> colnum <- lapply(col1, as.numeric)
> >>
> >> (The 2nd line assumes that the damage has already been done so
that
> >> you have aa_2000 ... aa_2007 in your workspace. You might
> >> alternatively create the list directly while importing the data.)
> >>
> >> -pd
> >>
> >>> On 4 Dec 2017, at 12:33 , Love Bohman <love.bohman at
sociology.su.se>
> wrote:
> >>>
> >>> Hi R-users!
> >>> Being new to R, and a fairly advanced Stata-user, I guess part
of my
> problem is that my mindset (and probably my language as well) is wrong.
> Anyway, I have what I guess is a rather simple problem, that I now without
> success spent days trying to solve.
> >>>
> >>> I have a bunch of datasets imported from Stata that is
labelled
> aa_2000 aa_2001 aa_2002, etc. Each dataset is imported as a matrix, and
> consists of one column only. The columns consists of integer numbers. I
> need to convert the data to vectors, which I found several ways to do. I
> use, for example:
> >>> aa_2000 <- as.numeric(aa_2000[,1])
> >>> However, when trying to automate the task, so I don't have
to write a
> line of code for each dataset, I get stuck. Since I'm a Stata user, my
> first attempt is trying to make a loop in order to loop over all datasets.
> However, I manage to write a loop that works for the left-hand side of the
> syntax, but not for the right-hand side.
> >>> I have included some examples from my struggles to solve the
issue
> below, what they all have in common is that I don't manage to call for
any
> "macro" (is that only a Stata-word?) in the right hand side of
the
> functions. When I try to replace the static reference with a dynamic one
> (like in the left-hand side), the syntax just doesn't work.
> >>>
> >>> I would very much appreciate some help with this issue!
> >>> All the best,
> >>> Love
> >>>
> >>> year <- 2002
> >>> dataname <- paste0("aa_",year)
> >>> assign(paste0(dataname), as.numeric(aa_2002[,1]))
> >>>
> >>> year <- 2003
> >>> assign(paste0("aa_",year), as.numeric(aa_2003))
> >>>
> >>> year <- 2005
> >>> assign(paste0("aa_",year), aa_2005[,1])
> >>>
> >>> list1 <- c(2000:2007)
> >>> list1[c(7)]
> >>> assign(paste0("aa_",list1[c(7)]),
as.numeric(paste0(aa_2006)))
> >>>
> >>>
> >>>     [[alternative HTML version deleted]]
> >>>
> >>> ______________________________________________
> >>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and
more, see
> >>> 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.
> >>
> >> --
> >> Peter Dalgaard, Professor,
> >> Center for Statistics, Copenhagen Business School Solbjerg Plads
3,
> >> 2000 Frederiksberg, Denmark
> >> Phone: (+45)38153501
> >> Office: A 4.23
> >> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> > --
> > Peter Dalgaard, Professor,
> > Center for Statistics, Copenhagen Business School Solbjerg Plads 3,
2000
> Frederiksberg, Denmark
> > Phone: (+45)38153501
> > Office: A 4.23
> > Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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.
>
> ------------------------------------------------------------
> ---------------
> Jeff Newmiller                        The     .....       .....  Go Live...
> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.
Live
> Go...
>                                        Live:   OO#.. Dead: OO#..  Playing
> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
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>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

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