[R] Modifying dataframe with mutate()

[Patrick (Malone Quantitative)]

Oh, right--I puzzled out my mistake.

On Sat, Jul 25, 2020 at 4:17 PM Jeff Newmiller <jdnewmil using dcn.davis.ca.us>
wrote:

> False. Mutate is similar in structure to the base function `within`. Which
> is why you have to assign the altered data frame back onto itself.
>
> On July 25, 2020 12:59:06 PM PDT, "Patrick (Malone Quantitative)" <
> malone using malonequantitative.com> wrote:
> >Jeff,
> >
> >mutate(), which is I think part of dplyr, also violates this, for what
> >it's
> >worth. I suspect the breaking point is that mutate() is intended to
> >create
> >new columns in the dataframe, not alter existing ones.
> >
> >On Sat, Jul 25, 2020 at 3:52 PM Jeff Newmiller
> ><jdnewmil using dcn.davis.ca.us>
> >wrote:
> >
> >> R is largely a functional language. You do something to an input and
> >end
> >> up with an output that has no effect on the input. This is actually a
> >> highly desirable feature.
> >>
> >> If you want your df variable to reflect changes made then you  need
> >to
> >> assign your result back into it.
> >>
> >> df <- df %>% mutate(v1 = as.double(v1))
> >>
> >> (Note that the data.table package violates this principle and is
> >> controversial as a result.)
> >>
> >> On July 25, 2020 12:11:24 PM PDT, H <agents using meddatainc.com> wrote:
> >> >In a statement like:
> >> >
> >> >df %>% mutate(v1 = as.double(v1))
> >> >
> >> >I expect the variable v1 in dataframe df to have been converted into
> >a
> >> >double. However, when I do:
> >> >
> >> >str(df)
> >> >
> >> >v1 still shows as int. Do I need to save the modified dataframe
> >after
> >> >mutating a variable?
> >> >
> >> >______________________________________________
> >> >R-help using 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.
> >>
> >> --
> >> Sent from my phone. Please excuse my brevity.
> >>
> >> ______________________________________________
> >> R-help using 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.
> >>
>
> --
> Sent from my phone. Please excuse my brevity.
>


-- 
Patrick S. Malone, Ph.D., Malone Quantitative
NEW Service Models: http://malonequantitative.com

He/Him/His

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