[R] which.max2()

2008-05-09 Thread Esmail Bonakdarian 

Hello,

which.max() only returns one index value, the one for the
maximum value. If I want the two index values for the two
largest values, is this a decent solution, or is there a
nicer/better R'ish way?

max2 -function(v)
{
m=which.max(v)
v[m] = -v[m]
m2=which.max(v)
result=c(m, m2)
result
}

Seems to work ok.

Thanks,
Esmail

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Re: [R] which.max2()

2008-05-09 Thread Dimitris Rizopoulos 

try this:

v - rnorm(10)
v
order(v, decreasing = TRUE)[1:2]


I hope it helps.

Best,
Dimitris


Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
http://www.student.kuleuven.be/~m0390867/dimitris.htm


- Original Message - 
From: Esmail Bonakdarian [EMAIL PROTECTED]

To: r-help@r-project.org
Sent: Friday, May 09, 2008 3:07 PM
Subject: [R] which.max2()



Hello,

which.max() only returns one index value, the one for the
maximum value. If I want the two index values for the two
largest values, is this a decent solution, or is there a
nicer/better R'ish way?

max2 -function(v)
{
m=which.max(v)
v[m] = -v[m]
m2=which.max(v)
result=c(m, m2)
result
}

Seems to work ok.

Thanks,
Esmail

__
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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.




Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

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Re: [R] which.max2()

2008-05-09 Thread Marc Schwartz 

on 05/09/2008 08:07 AM Esmail Bonakdarian wrote:

Hello,

which.max() only returns one index value, the one for the
maximum value. If I want the two index values for the two
largest values, is this a decent solution, or is there a
nicer/better R'ish way?

max2 -function(v)
{
m=which.max(v)
v[m] = -v[m]
m2=which.max(v)
result=c(m, m2)
result
}

Seems to work ok.

Thanks,
Esmail


I might be tempted to take a more generic approach, where one can
provide an argument to the function to indicate that I want the 'top x'
maximum values and to give the user the option of returning the indices 
or the values themselves.


Perhaps:

which.max2 - function(x, top = 1, values = FALSE)
{
  if (values)
rev(sort(x))[1:top]
  else
order(x, decreasing = TRUE)[1:top]
}

set.seed(1)
Vec - rnorm(10)

 Vec
 [1] -0.6264538  0.1836433 -0.8356286  1.5952808  0.3295078 -0.8204684
 [7]  0.4874291  0.7383247  0.5757814 -0.3053884


 which.max2(Vec, 2)
[1] 4 8

 which.max2(Vec, 2, values = TRUE)
[1] 1.5952808 0.7383247


HTH,

Marc Schwartz

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Re: [R] which.max2()

2008-05-09 Thread Esmail Bonakdarian 

Dimitris Rizopoulos wrote:

try this:

v - rnorm(10)
v
order(v, decreasing = TRUE)[1:2]


Wow .. that is slick! First I thought, wait .. I don't want to
reorder the elements, but this doesn't - it just returns the index
values in order. I don't really get that from reading the documentation,
it's probably there, but not that clear to me.

Thanks for showing me something more R'ish.

Esmail

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Re: [R] which.max2()

2008-05-09 Thread Esmail Bonakdarian 

Marc Schwartz wrote:


I might be tempted to take a more generic approach, where one can
provide an argument to the function to indicate that I want the 'top x'
maximum values and to give the user the option of returning the indices 
or the values themselves.


Perhaps:

which.max2 - function(x, top = 1, values = FALSE)
{
  if (values)
rev(sort(x))[1:top]
  else
order(x, decreasing = TRUE)[1:top]
}


Very cool too! .. Thanks Marc. Again, I did not get this from the
order documentation (ie that it manipulate index values rather than
the values themselves). Great to see examples.

Best,
Esmail

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