R help - Apr 2001 - how to do java-like hashtables in R, R from a java programmer's p onit of view

I suppose I am looking for recommendations on the right book on R for me.
This post drones on a bit about what sort of programming I do and is
basically asking if there are any books on R written with me in mind.  I
also make a proposal regarding R documentation at the end.

I started reading "Programming with Data," by Chambers, got really
excited
in chapter 1, then found that I had a hard time learning what I wanted to
know from the rest of it.

I have been reading "An Introduction to R," which is quite good, but
stops
short of what I want to know. My company operates a satellite mobile data
network and I am the "chief traffic analysist," you might say.  I have
a
packet sniffer that captures a complete record of every packet that goes
over the air in our network and from that, I study the system's capacity, do
troubleshooting, and all sorts of other analysis.  I plot things like
channel utilisation versus time during the day, arrival and departure rates
of calls in the system, arrival rates of different categories of packets,
and many other things.  I am no statistician (I'm a communictions theory guy
who enjoys programming).

I have written a lot of software to analyze the raw data in java and I am
very attracted to R's interactive ploting and data analysis abilities.  I am
having a hard time making the connection between how I usually do things in
java and how to do things in R, however.

After I got the basic syntax of R down, one of the first questions I asked
myself was."O.K., now how do I build a hashtable from a text file?"

I took me a while to realize that R's lists are one way to do that.

For example, suppose I have a text file with the following key/value pairs
in it
a,1
b,1
c,4
d,3
...

and I want to read this into a hash table.  I must have written a dozen
programs that do any number of variations on this basic task in the last
year or so.  I can't believe how useful it is.

In R, you might proceed as follows to build such a table.  Say x is some
list object.  Say you have a loop that is reading key/value pairs into the
variables "key" and "value" one after another.

Putting the pair in the table is as simple as:

x[[key]] <- value

Later, retrieving a value from a key would be:

x[[key]]


Are there any books that explain how to use the base packages in R or S to
do tasks like this?  I feel like I am really stumbling around in the dark
trying to slowly figure things out in R.

When writing a java program to perform some new type of analysis, I
typically lay out a few obvious classes based on the sorts of data I am
trying to extract and start filling in the details of the classes.  Is this
the right way to think of programming in R/S?

It occurs to me that some simple java programs and their corresponding R
implementations would be a very powerful form of documentation for java
programmers wanting to learn R.  This is my second attempt to come to grips
with R;  I tried and failed about a year ago.

Perhaps this forum would be an excellent place to develop such example
program translations?  I would certainly be willing to boil down some of my
typical java data analysis programs into short, clear examples, if anyone
would be interested in helping me translate them into R.

Chris Marshall
 
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Chris Marshall <chrism at norcomnetworks.com> writes:
> In R, you might proceed as follows to build such a table.  Say x is some
> list object.  Say you have a loop that is reading key/value pairs into the
> variables "key" and "value" one after another.
> 
> Putting the pair in the table is as simple as:
> 
> x[[key]] <- value
> 
> Later, retrieving a value from a key would be:
> 
> x[[key]]
Actually, the linear structure of a list in R makes this rather
inefficient. Another option is to use environments and pretend that
the key is a variable name:

e <- new.env()
assign(key,value,envir=e)
get(key,envir=e)

This has the advantage that environments, contrary to lists, really
are hashed. Take a peek inside envir.c if you care.

(Abandon all hopes of S-PLUS compatibility if you do this, though.
Also beware that environments are slightly strange objects since they
are never duplicated - e.g. on assignment.)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On Wed, 25 Apr 2001, Chris Marshall wrote:

[snip]

I do some *very* similar things, except that I do the data structuring in
Perl and create comma-separated value files that I can read directly into
R with "read.csv". The basic data structure in R is the data frame,
and most
of my Perl code simply builds data frames.

I have actually processed sniffer-like data. In the specific case, I simply
built a list indexed by time stamp in milliseconds (column 1). Column 2 is the
"from" IP address, column 2 is to "to" IP address, column 3
is the byte count
and column 4 is the protocol. In actuality, my data came from Microsoft SMS
NetMon rather than from a sniffer. Then all I have to do is read the data into
a statistics package (when I did this I used Minitab, not R) and I can easily
do analysis on packets by source, destination, protocol, etc. Contact me off-
list for more details.
--
znmeb at aracnet.com (M. Edward Borasky) http://www.aracnet.com/~znmeb

How to Stop A Folksinger Cold # 3
"If you miss the train I'm on..."
Tough.

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._