# [R] matrix from sequences

Spencer Graves spencer.graves at pdf.com
Fri Feb 14 22:19:06 CET 2003

```Hi, Miha:

1.  How do I get the GRASS library?  "library(GRASS)" produced "Error in
library(GRASS) : There is no package called `GRASS'" for me from R 1.6.2
for Windows.

2.  I assume there is a typographical error in the last line of your
email:  If G\$xseq and \$yseq are coordinates of points, then
length(G\$xseq) == length(G\$yseq)???  In that case,
'as.matrix(G[,c("xseq", "yseq")])' should give you what you want.

Or am I missing something?
Best Wishes,
Spencer Graves

Miha STAUT wrote:
>> Miha STAUT wrote:
>>
>>> Hi all,
>>>
>>> I have a data frame with sequences of x and y from a map. I would
>>> like to know it both ways:
>>> 1. How to make a matrix from that;
>>> 2. how to make a data frame of all points in a map.
>>>
>>> Probably it is a silly question, but please tell me where to read
>>> about it or tell me how to do it.
>>>
>>> Miha Staut
>>>
>>> ______________________________________________
>>> R-help at stat.math.ethz.ch mailing list
>>> http://www.stat.math.ethz.ch/mailman/listinfo/r-help
>>>
>> Hi Miha,
>>
>> 1) What is the structure of your data.frame ? Assuming all
>> co-ordinates are in the same column (one column for x and one column
>> for y), the simplest way to extract them and turn them into a matrix
>> would be:
>>
>> as.matrix(mydata[ , c("x", "y")])
>>
>> e.g.:
>>
>> R>mydata <- data.frame(x = rnorm(10), y = rnorm(10), z = rnorm(10))
>> R>mydata
>>              x           y          z
>> 1  -0.73735224 -0.51218243 -0.9602624
>> 2  -1.46079091 -0.63634091  1.4967066
>> 3  -0.28574919 -1.30719383 -0.2887403
>> 4   0.04137159  0.61711350 -0.7057102
>> 5   0.03179303  0.05734869 -0.4637660
>> 6  -0.06638058 -0.74565157  0.9239402
>> 7  -0.67611541 -1.01760810 -0.2854017
>> 8   0.34215052  0.30564550  0.6931193
>> 9   0.83597837  0.75443762 -2.3394679
>> 10 -0.14967073 -0.02027512 -0.1143414
>> R>as.matrix(mydata[ , c("x", "y")])
>>              x           y
>> 1  -0.73735224 -0.51218243
>> 2  -1.46079091 -0.63634091
>> 3  -0.28574919 -1.30719383
>> 4   0.04137159  0.61711350
>> 5   0.03179303  0.05734869
>> 6  -0.06638058 -0.74565157
>> 7  -0.67611541 -1.01760810
>> 8   0.34215052  0.30564550
>> 9   0.83597837  0.75443762
>> 10 -0.14967073 -0.02027512
>>
>>
>> 2) How are the points stored ? If in a matrix, say mat, with 2 columns
>> for x and y, simply:
>>
>> as.data.frame(mat)
>>
>> Best,
>>
>> Renaud
>
>
>
> Thanks to both of you (Dr Renaud Lancelot and James Holtman)
>
> I see I formulated the question in a wrong way. I got from GRASS the
> coordinates of a map. There is a package in R named GRASS to connect R
> with GRASS.
>
> library(GRASS)
> G<-gmeta() # copy the environment from GRASS
>
> Now G is a data frame containig also \$xseq and \$yseq which would be the
> coordinates of all the points in x and y direction. The final matrix
> should have length(G\$xseq) * length(G\$yseq) points.
>
> Miha Staut
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-help

```