[R] Taking the sum of only some columns of a data frame

[Bert Gunter]

All:

1. I agree wholeheartedly with prior responses.

2. But let's suppose that for some reason, you *did* want to carry
around some "calculated values" with the data frame. Then one way to
do it is to add them as attributes to the data frame. This way they
cannot "pollute" the data in the way Jeff warned against; e.g.

attr(your_frame,"colsums") <- colSums(your_frame)

This of course calculates them all, but you can of course just attach
some (e.g. colSums(your_frame[,c(1,3)] )

3. This, of course, has the disadvantage of requiring recalculation of
the attribute if the data changes, which is an invitation to problems.
A better approach might be to attach the *function* that does the
calculation as an attribute, which when invoked always uses the
current data:

attr(your_frame,"colsums") <- function(x)colSums(x)

For example:

df <- data.frame(x=1:5,y=21:25)
attr(df,"colsums")<- function(x)colSums(x)

## then:
> attr(df,"colsums")(df)
  x   y
 15 115

## add a row
> df[6,] <- rep(100,2)
> attr(df,"colsums")(df)
  x   y
115 215


This survives changing the name of df:

> dat <- df
> attr(dat,"colsums")(dat)
  x   y
115 215

As it stands, the call: attr(df,"colsums")(df)  is a bit clumsy; one
could easily write a function that does this sort of thing more
cleanly, as, for example, is done via the "selfStart" functionality
for nonlinear models.

But all this presupposes that the OP is familiar with R programming
paradigms, especially the use of functions as first class objects, and
the language in general. While I may have missed this, his posts do
not seem to me to indicate such familiarity, so as others have
suggested, perhaps the best answer is to first spend some time with an
R tutorial or two and *not* try to mimic bad spreadsheet practices in
R.

Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Mar 31, 2017 at 2:49 PM, Jeff Newmiller
<jdnewmil at dcn.davis.ca.us> wrote:
> You can also look at the knitr-RMarkdown work flow, or the knitr-latex work flow. In both of these it is reasonable to convert your data frame to a temporary character-only form purely for output purposes. However, one can usually use an existing function to push your results out without damaging your working data.
>
> It is important to separate your data from your output because mixing results (totals) with data makes using the data further extremely difficult. Mixing them is one of the major flaws of the spreadsheet model of computation, and it causes problems there as well as in R.
> --
> Sent from my phone. Please excuse my brevity.
>
> On March 31, 2017 1:05:09 PM PDT, William Michels via R-help <r-help at r-project.org> wrote:
>>Again, you should always copy the R-help list on replies to your OP.
>>
>>The short answer is you **shouldn't** replace NAs with blanks in your
>>matrix or dataframe.  NA is the proper designation for those cell
>>positions. Replacing NA with a "blank" in a dataframe will convert
>>that column to a "character" mode, precluding further numeric
>>manipulation of those columns.
>>
>>Consider your workflow:  are you tying to export a table? If so, take
>>a look at installing pander (see 'missing' argument on webpage below):
>>
>>https://cran.r-project.org/web/packages/pander/README.html
>>
>>Finally, please review the Introductory PDF, available here:
>>
>>https://cran.r-project.org/doc/manuals/R-intro.pdf
>>
>>HTH, Bill.
>>
>>William Michels, Ph.D.
>>
>>
>>
>>On Fri, Mar 31, 2017 at 11:21 AM, BR_email <br at dmstat1.com> wrote:
>>> William:
>>> How can I replace the "NAs" with blanks?
>>> Bruce
>>>
>>> Bruce Ratner, Ph.D.
>>> The Significant Statistician™
>>>
>>>
>>> William Michels wrote:
>>>>
>>>> I'm sure there are more efficient ways, but this works:
>>>>
>>>>> test1 <- matrix(runif(50), nrow=10, ncol=5)
>>>>> ## test1 <- as.data.frame(test1)
>>>>> test1 <- rbind(test1, NA)
>>>>> test1[11, c(1,3)] <- colSums(test1[1:10,c(1,3)])
>>>>> test1
>>>>
>>>>
>>>> HTH,
>>>>
>>>> Bill.
>>>>
>>>> William Michels, Ph.D.
>>>>
>>>>
>>>>
>>>> On Fri, Mar 31, 2017 at 9:20 AM, Bruce Ratner PhD <br at dmstat1.com>
>>wrote:
>>>>>
>>>>> Hi R'ers:
>>>>> Given a data.frame of five columns and ten rows.
>>>>> I would like to take the sum of, say, the first and third columns
>>only.
>>>>> For the remaining columns, I do not want any calculations, thus
>>rending
>>>>> their "values" on the "total" row blank. The sum/total row is to be
>>combined
>>>>> to the original data.frame, yielding a data.frame with five columns
>>and
>>>>> eleven rows.
>>>>>
>>>>> Thanks, in advance.
>>>>> Bruce
>>>>>
>>>>>
>>>>> ______________
>>>>> Bruce Ratner PhD
>>>>> The Significant Statistician™
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>          [[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.