R help - Aug 2019 - Trying to understand how to sort a DF on two columns

I want to sort a DF, temp, on two columns, patid and time. I have searched the
internet and found code that I was able to modify to get my data sorted.
Unfortunately I don't understand how the code works. I would appreciate it
if someone could explain to me how the code works. Among other questions,
despite reading, I don't understand how with() works, nor what it does in
the current setting.

code:
data4xsort<-temp[
  with( temp, order(temp[,"patid"], temp[,"time"])),
]

Thank you,
John





John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric
Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)


	[[alternative HTML version deleted]]

https://stackoverflow.com/questions/2315601/understanding-the-order-function

Do a web search on "How does order() work R" or similar for more.

I can't explain with() any better than the docs: saying that it evaluates
the expression argument in the data argument environment -- a data frame
for the data frame method -- probably won't help you.

-- 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 Mon, Aug 12, 2019 at 7:20 PM Sorkin, John <jsorkin at
som.umaryland.edu>
wrote:
> I want to sort a DF, temp, on two columns, patid and time. I have searched
> the internet and found code that I was able to modify to get my data
> sorted. Unfortunately I don't understand how the code works. I would
> appreciate it if someone could explain to me how the code works. Among
> other questions, despite reading, I don't understand how with() works,
nor
> what it does in the current setting.
>
> code:
> data4xsort<-temp[
>   with( temp, order(temp[,"patid"], temp[,"time"])),
> ]
>
> Thank you,
> John
>
>
>
>
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
> Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
>         [[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.
>
	[[alternative HTML version deleted]]

On 8/12/19 7:20 PM, Sorkin, John wrote:
> I want to sort a DF, temp, on two columns, patid and time. I have searched
the internet and found code that I was able to modify to get my data sorted.
Unfortunately I don't understand how the code works. I would appreciate it
if someone could explain to me how the code works. Among other questions,
despite reading, I don't understand how with() works, nor what it does in
the current setting.
>
> code:
> data4xsort<-temp[
>    with( temp, order(temp[,"patid"], temp[,"time"])),
> ]
>
> Thank you,
> John

The `order`-function returns a numeric vector which is the length of its 
inputs (and there is recycling when the inputs are of different length). 
The numbers are the order in which the items would be if they were 
sorted smallest to largest. There are arguments that let you control the 
behavior in the case of ties. So when used in an indexing application as 
seen here, it results in the dataframe returned with its rows in 
ascending order based primarily on its first argument, patid,? and in 
case of ties on the second argument, time. If you put a minus sign in 
from of the argument it the ordering is largest to smallest.


If that is code you are getting from elsewhere, you should realize that 
it is somewhat redundant and you should question the level of R skills 
of its author.? In this code it is doing absolutely nothing. The `with( 
...) is not needed because the arguments already have an unambiguous 
place to get the column names.? A more compact expression if you were 
going to use `with` would be:

data4xsort<-temp[ with( temp, order(patid, time)), ]

But using `with` carries risks because there are sometimes confusion about which
environment it will find the named objects or columns.

Safer would be to not using it in this situation.

Your headers suggest you are using Outlook. Surely there must be a way to
specify a plain text format for outgoing emails. This is a plain text mailing
list.

David.
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
> 	[[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.

Bert,

Thank you for your reply (and the many other questions to the list that you
answer).

I understand how order works when ordering based on a single column. What I
don?t understand is how the code I included with my email works. I believe my
problem is a lack of understanding of what with does. I have read about the with
function, but I must be missing something.

Thank you,
John

From: Bert Gunter <bgunter.4567 at gmail.com>
Sent: Monday, August 12, 2019 10:36 PM
To: Sorkin, John <jsorkin at som.umaryland.edu>
Cc: r-help at r-project.org (r-help at r-project.org) <r-help at
r-project.org>
Subject: Re: [R] Trying to understand how to sort a DF on two columns

https://stackoverflow.com/questions/2315601/understanding-the-order-function

Do a web search on "How does order() work R" or similar for more.

I can't explain with() any better than the docs: saying that it evaluates
the expression argument in the data argument environment -- a data frame for the
data frame method -- probably won't help you.

-- 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 Mon, Aug 12, 2019 at 7:20 PM Sorkin, John <jsorkin at
som.umaryland.edu<mailto:jsorkin at som.umaryland.edu>> wrote:
I want to sort a DF, temp, on two columns, patid and time. I have searched the
internet and found code that I was able to modify to get my data sorted.
Unfortunately I don't understand how the code works. I would appreciate it
if someone could explain to me how the code works. Among other questions,
despite reading, I don't understand how with() works, nor what it does in
the current setting.

code:
data4xsort<-temp[
  with( temp, order(temp[,"patid"], temp[,"time"])),
]

Thank you,
John





John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric
Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)


        [[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org<mailto: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.

	[[alternative HTML version deleted]]

Hello,

Though good answers were already given, I would like to say something.

1.
If you are lazy (typing), use with, if you prefer to play safe, don't.
I am lazy many times, but in interactive mode only.

2.
I find it better in the long run *not* to take advantage of R's 
one-liners, they tend to be less readable. Instead of putting everything 
in the same instruction why not

i <- order( temp$patid, temp$time )
data4xsort <- temp[ i, ]


This has the disadvantage of creating an extra variable but are you 
really having memory problems? If not, use the clearer code. Besides, if 
this goes into a function all temporary variables will be gone and the 
memory released, in which case there will be no problem.

(The with equivalent is i <- with(temp, order(patid, time)), btw.)

Hope this helps,

Rui Barradas

?s 03:20 de 13/08/19, Sorkin, John escreveu:
> I want to sort a DF, temp, on two columns, patid and time. I have searched
the internet and found code that I was able to modify to get my data sorted.
Unfortunately I don't understand how the code works. I would appreciate it
if someone could explain to me how the code works. Among other questions,
despite reading, I don't understand how with() works, nor what it does in
the current setting.
> 
> code:
> data4xsort<-temp[
>    with( temp, order(temp[,"patid"], temp[,"time"])),
> ]
> 
> Thank you,
> John
> 
> 
> 
> 
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
> 
> 
> 	[[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.
>