[R] About change columns and specific rows in R

lily li
Tue, 23 May 2017 16:31:51 -0000

Thanks for all your help. It works now.

On Tue, May 23, 2017 at 1:34 AM, William Michels via R-help <
r-help at r-project.org> wrote:

> Hi Ivan,
>
> I was just writing a follow-up note as your note came in. While the
> code I posted previously works fine, using which() is unnecessary.
>
> > DF <- read.csv("~/lily.csv")
> > DF$product1_1 <- NA
> > DF$product1_1 <- DF[DF$month == 1, "product1"]*3.1
> Error in `$<-.data.frame`(`*tmp*`, "product1_1", value =
c(55.8, 58.9,  :
>   replacement has 4 rows, data has 7
> > DF$product1_1 <- DF[which(DF$month == 1), "product1"]*3.1
> Error in `$<-.data.frame`(`*tmp*`, "product1_1", value =
c(55.8, 58.9,  :
>   replacement has 4 rows, data has 7
> > DF[DF$month == 1, "product1_1"] <- DF[DF$month == 1,
"product1"]*3.1
> > DF
>   year month day product1 product2 product3 product1_1
> 1 1981     1   1       18       56       20       55.8
> 2 1981     1   2       19       45       22       58.9
> 3 1981     1   3       16       48       28       49.6
> 4 1981     1   4       19       50       21       58.9
> 5 1981     2   1       17       49       25         NA
> 6 1981     2   2       20       47       23         NA
> 7 1981     2   3       21       52       27         NA
> >
>
> The two errors above were caused because I failed to specify rows on
> the left hand side of the assignment operator, not because I failed to
> use which(). Once rows and columns are specified on both sides, the
> assignment works fine.
>
> (I do however, prefer to create an "NA" column first. Personal
preference
> ;-).
>
> Best Regards,
>
> Bill.
>
>
>
> On Mon, May 22, 2017 at 11:57 PM, Ivan Calandra <calandra at rgzm.de>
wrote:
> > Hi,
> >
> > Actually, you don't need to create the column first, nor to use
which:
> > DF[DF$month==1, "product1_1"] = DF[DF$month==1,
"product1"] * 3.1
> >
> > The "[" is a great tool that you need to learn. In this
case, you don't
> need
> > to combine "[" and $: within the square brackets, the vector
before the
> > comma indexes the rows and the one after the comma indexes the
columns.
> >
> > The other thing you were missing correctly referencing the rows. You
> have to
> > specify the data.frame you want to look into.
> >
> > And last, learn to use dput() to provide a nice reproducible example.
> >
> > HTH,
> > Ivan
> >
> >
> > --
> > Dr. Ivan Calandra
> > TraCEr, Laboratory for Traceology and Controlled Experiments
> > MONREPOS Archaeological Research Centre and
> > Museum for Human Behavioural Evolution
> > Schloss Monrepos
> > 56567 Neuwied, Germany
> > +49 (0) 2631 9772-243
> > https://www.researchgate.net/profile/Ivan_Calandra
> >
> > On 23/05/2017 08:45, William Michels via R-help wrote:
> >>
> >> Hi Lily,
> >>
> >> You're on the right track, but you should define a new column
first
> >> (filled with NA values), then specify the precise rows and columns
on
> >> both the left and right hand sides of the assignment operator that
> >> will be altered. Luckily, this is pretty easy...just remember to
use
> >> which() on the right hand side of the assignment operator to get
the
> >> index of the rows you want. Example below for
"product1":
> >>
> >>> DF$product1_1 <- NA
> >>> DF[DF$month == 1, "product1_1"] <-
DF[which(DF$month == 1),
> >>> "product1"]*3.1
> >>>
> >>
> >> HTH,
> >>
> >> Bill.
> >>
> >> William Michels, Ph.D.
> >>
> >>
> >>
> >>
> >> On Mon, May 22, 2017 at 9:56 PM, lily li <chocold12 at
gmail.com> wrote:
> >>>
> >>> Hi R users,
> >>>
> >>> I have a question about manipulating the dataframe. I want to
create a
> >>> new
> >>> dataframe, and to multiply rows with different seasons for
different
> >>> constants.
> >>>
> >>> DF
> >>> year   month   day   product1   product2   product3
> >>> 1981     1          1         18              56            20
> >>> 1981     1          2         19              45            22
> >>> 1981     1          3         16              48            28
> >>> 1981     1          4         19              50            21
> >>> 1981     2          1         17              49            25
> >>> 1981     2          2         20              47            23
> >>> 1981     2          3         21              52            27
> >>>
> >>> For example, how to multiply product1 in month1 by 3.1, and to
multiply
> >>> product3 in month2 by 2.0? I wrote the code like this but does
not
> work.
> >>> Thanks for your help.
> >>>
> >>> DF['month'==1, ]$product1_1 = DF['month'==1,
]$product1 * 3.1;
> >>> DF['month'==2, ]$product3_1 = DF['month'==1,
]$product3 * 2.0;
> >>>
> >>>          [[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.
> >>
> >> ______________________________________________
> >> 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.
> >>
> >
> > ______________________________________________
> > 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.
>
> ______________________________________________
> 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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