[R] Modifying dataframe with mutate()

[Jeff Newmiller]

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?
>> >
>> >______________________________________________
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>> >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
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>> 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.