[R] help to make a map on R

[Don MacQueen]

If I understand the question correctly, the solution is simpler than 
some of the other suggestions. Here is what I would do.

First, here is an example data file:

traj	lat	long
T	2.1	3.4
T	4.2	5.1
T	3.6	6.2
T	4.2	5.1

T	11.4	12.3
T	13.2	14.8
T	9.3	11.2

T	19.4	20.3
T	21.3	16.8
T	22.3	15.6
T	23.1	14.4

T	34.2	32.3
T	39.2	34.8
T	39.3	31.2

Next, here is a script to make the plot:

## read the data (the delimiter is tab character in this example)
dat <- read.delim('junk.dat',colClasses=c('character','numeric','numeric'),
                   blank.lines.skip=FALSE)

## change "T" to "T1", "T2" etc.
rl <- rle(dat$traj)
dat <- dat[dat$traj != '',]
lens <- rl$lengths[rl$lengths != 1]
dat$traj <- paste(dat$traj,
                   rep(1:lens),lens),
                   sep='')

## function for plotting lines
lfun <- function(df) lines(df$long,df$lat)

## prepare an empty plot with the correct range
ylm <- range(dat$lat)
xlm <- range(dat$long)
plot(xlm,ylm,type='n')

## add the lines to the plot, one line for each trajectory
lapply(split(dat,dat$traj),lfun)

Since you have about 3000 trajectories, the lapply() step may take a long time.

The essential steps are the use of the rle() and rep() functions. 
That, and including the blank lines while reading the data file.

Very important warning: this method assumes that whenever there is a 
blank line there is only one blank line. Never two or more blank 
lines next to each other.

I hope this helps
-Don

At 4:26 PM -0300 10/2/02, Ronaldo Reis Jr. wrote:
>Hi all,
>I need a little help for construct an state's map on R.
>
>The first problem is to get the data.
>
>I have a datafile of longitude and latitude in the follow format:
>
>trajectory	latitude	longtude
>T		-22.045618	-51.287056
>T		-22.067078	-51.265888
>T		-22.067039	-51.207249
>
>T		-22.059690	-48.089695
>T		-22.075529	-48.074608
>T		-22.072460	-48.044472
>
>T		-22.062767	-48.298473
>T		-22.077349	-48.322140
>T		-22.047001	-48.347443
>T		-22.054266	-48.369331
>T		-22.042810	-48.392612
>T		-22.064812	-48.422195
>T		-22.062544	-48.443497
>
>To read a file is simple, but I need that R change the value of
>trajectory after a blank line, reading something like this:
>
>trajectory	latitude	longitude
>T1		-22.045618	-51.287056
>T1		-22.067078	-51.265888
>T1		-22.067039	-51.207249
>T2		-22.059690	-48.089695
>T2		-22.075529	-48.074608
>T2		-22.072460	-48.044472
>T3		-22.062767	-48.298473
>T3		-22.077349	-48.322140
>T3		-22.047001	-48.347443
>T3		-22.054266	-48.369331
>T3		-22.042810	-48.392612
>T3		-22.064812	-48.422195
>T3		-22.062544	-48.443497
>
>Each trajectory is a line that is a little piece of my map.
>
>After this, to make a map I execute:
>
>tapply() for separate the coordinates for each trajectory, something like
>this:
>
>>  longitude <- tapply(longitude,trajectory,c)
>>  longitude
>$T1
>[1] -51.2871 -51.2659 -51.2072
>
>$T2
>[1] -48.0897 -48.0746 -48.0445
>
>$T3
>[1] -48.2985 -48.3221 -48.3474 -48.3693 -48.3926 -48.4222 -48.4435
>
>>  latitude <- tapply(latitude,trajectory,c)
>>  latitude
>$T1
>[1] -22.0456 -22.0671 -22.0670
>
>$T2
>[1] -22.0597 -22.0755 -22.0725
>
>$T3
>[1] -22.0628 -22.0773 -22.0470 -22.0543 -22.0428 -22.0648 -22.0625
>
>The nest step is to make a plot with the coordinates.
>
>>  plot(longitude,latitude, asp = 1, type = "n")
>
>And finally plot the lines for each trajectory, and all lines together,
>make a Sao Paulo's map and your cities limits.
>
>>  lines(longitude$T1,latitude$T1)
>>  lines(longitude$T2,latitude$T2)
>>  lines(longitude$T3,latitude$T3)
>
>How can I make to automatized this process? Because I can about 3000
>trajectory.
>
>Any other idea for make this is welcome.
>
>
>Thanks for all
>
>Inte mais
>Ronaldo

-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
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