[R] matrix from sequences
Miha STAUT
mihastaut at hotmail.com
Fri Feb 14 21:53:03 CET 2003
>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
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