question on mean, sum

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question on mean, sum

mokuram
 Hi,
I am working on functions such as sum(), mean() ...
> sum(mtcars)[1] 13942.2> mean(mtcars)[1] NAWarning message:In mean.default(mtcars) : NA> sd(mtcars)Error in is.data.frame(x) : ()'double'
why got different reply?Is this a BUG for the current version of R?my version info:version.string R version 3.3.1 (2016-06-21)

Thank you very much for the help.
mokuram

        [[alternative HTML version deleted]]

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Re: question on mean, sum

PIKAL Petr
Hi

Your HTML formatted message is scrambled so it is hard to understand what is your problem. The probable cause is the fact that sum, mean and sd behave differently when applied to different objects (vector, data.frame, ...)

Post in plain text together with at least result of
str(mtcars)

Cheers
Petr


> -----Original Message-----
> From: R-help [mailto:[hidden email]] On Behalf Of
> [hidden email]
> Sent: Monday, November 14, 2016 4:01 AM
> To: r-help <[hidden email]>
> Subject: [R] question on mean, sum
>
>  Hi,
> I am working on functions such as sum(), mean() ...
> > sum(mtcars)[1] 13942.2> mean(mtcars)[1] NAWarning message:In
> mean.default(mtcars) : NA> sd(mtcars)Error in is.data.frame(x) : ()'double'
> why got different reply?Is this a BUG for the current version of R?my version
> info:version.string R version 3.3.1 (2016-06-21)
>
> Thank you very much for the help.
> mokuram
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] 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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Re: question on mean, sum

Berend Hasselman
In reply to this post by mokuram

In addition to Petr's remarks:

- why are you doing sum(mtcars)[1]?  Do you want the sum of first column of mtcars? In that case you should do sum(mtcars[,1]).

- similar remarks apply to your use of  mean and sd.


Have you read an introduction to R?


Berend

> On 14 Nov 2016, at 04:01, [hidden email] wrote:
>
> Hi,
> I am working on functions such as sum(), mean() ...
>> sum(mtcars)[1] 13942.2> mean(mtcars)[1] NAWarning message:In mean.default(mtcars) : NA> sd(mtcars)Error in is.data.frame(x) : ()'double'
> why got different reply?Is this a BUG for the current version of R?my version info:version.string R version 3.3.1 (2016-06-21)
>
> Thank you very much for the help.
> mokuram
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] 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.

______________________________________________
[hidden email] 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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Re: question on mean, sum

Jim Lemon-4
In reply to this post by mokuram
Hi mokuram,

As others have noted, you will profit from a bit more knowledge about
"extraction":

sum(mtcars)
[1] 13942.2

This works because you have "extracted" the first column of the
"mtcars" data frame _as a data frame_

mtcars[1]
                    mpg
Mazda RX4           21.0
Mazda RX4 Wag       21.0
...
Volvo 142E          21.4

is.data.frame(mtcars[1])
[1] TRUE

mean(mtcars)
[1] NA
Warning message:
In mean.default(mtcars) :
argument is not numeric or logical: returning NA

Here you are trying to take the mean of the entire data frame. While
the mean function will "coerce" a single column to a vector, it won't
do so for an entire data frame. However, if you coerce the data frame
to a matrix:

mean(as.matrix(mtcars))
[1] 39.60853

That's the good news. The bad news is that the result is meaningless.
The same thing goes for:

sd(as.matrix(mtcars))
[1] 84.20792

It is almost always a good idea to read the error messages carefully
and try to understand them.

Jim


On Mon, Nov 14, 2016 at 2:01 PM,  <[hidden email]> wrote:

>  Hi,
> I am working on functions such as sum(), mean() ...
>> sum(mtcars)[1] 13942.2> mean(mtcars)[1] NAWarning message:In mean.default(mtcars) : NA> sd(mtcars)Error in is.data.frame(x) : ()'double'
> why got different reply?Is this a BUG for the current version of R?my version info:version.string R version 3.3.1 (2016-06-21)
>
> Thank you very much for the help.
> mokuram
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] 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.

______________________________________________
[hidden email] 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.