From: Dimitris Rizopoulos
Hi Bryan,
1. which(x==1)
2. X[2:nrow(X),] or X[,2:ncol(X)]
The "An Introduction to R" document is very usdeful for this kind of
things.
I hope it helps.
Best,
Dimitris
----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message -----
From: "Bryan L. Brown" <stonefly at mail.utexas.edu>
To: <R-help at stat.math.ethz.ch>
Sent: Thursday, October 07, 2004 4:10 PM
Subject: [R] Equivalents of Matlab's 'find' and 'end'
Sorry if these questions have been asked recently--I'm new to this
list.
I'm primarily a Matlab user who is attempting to learn R and I'm
searching for possible equivalents of commands that I found very
handy in Matlab. So that I don't seem ungrateful to those who may
answer, I HAVE determined ways to carry out these processes in
'brute force' sorts of ways in R code, but they lack the elegance
and simplicity of the Matlab commands. Also, if you know that no
such commands exist, that bit of knowledge would be helpful to know
so that I don't continue fruitless searches.
The first is Matlab's 'find' command.
This is one of the most useful commands in Matab. Basically, if X
is the vector
X=[3, 2, 1, 1, 2, 3]
the command
'find(X==1)'
would return the vector [3, 4] which would indicate that the vector
X had the value of 1 at the 3 and 4 positions. This was an
extremely useful command for subsetting in Matlab. The closest
thing I've found in R has been 'match' but match only returns the
first value as opposed to the position of all matching values.
The second Matlab command that I'd like to find an R equivalent for
is 'end'. 'end' is just a simple little command that indicates the
end of a row/column. It is incredibly handy when used to subset
matrices like
Y = X(2:end)
and produces Y=[2, 1, 1, 2, 3] if the X is the same as in the
previous example. This cutsie little command was extremely useful
for composing programs that were flexible and could use input
matrices of any size without modifying the code. I realize
can accomplish the same by Y <- X[2:length(X)] in R, but
is ungainly, particularly when subsetting matrices rather than
vectors.
If anyone has advice, I'd be grateful,
Bryan L. Brown
Integrative Biology
University of Texas at Austin
Austin, TX 78712
512-965-0678
stonefly at mail.utexas.edu
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