[R] lines()

[Duncan Murdoch]

On 23/11/2012 11:56 AM, wdmc2012 wrote:
> I have some latitude and longitudes that I am trying to plot on an image with the lines() command like this:
>
> image(seq(-98, -93, 0.1), seq(28.5, 32.5, 0.1), z, xlab= "Longitude", ylab= "Latitude", main= "Temperature")
> for (i in 2:length(subset(geo, Feature=="Coast")[,1])) {
> lines(x=geo[(i-1),2]:geo[i,2], y=geo[(i-1),1]:geo[i,1], col="blue", lwd=3) }

The expression

x=geo[(i-1),2]:geo[i,2]

probably isn't what you intended.  It is the sequence of values from 
geo[(i-1),2] to geo[i,2], taking integer steps.  E.g. 1.2:1.8
just gives the single value 1.2; 1.2:3.4 gives the sequence 1.2, 2.2, 3.2.

I would guess you wanted

x=c(geo[(i-1),2], geo[i,2])

instead; it's the pair of points.

I think there's another error here too; you let i range over the rows of a subset of geo, but then plot values from the original matrix/dataframe.

Duncan Murdoch


>
> There aren't any errors, but nothing shows up on the plot. I tried substituting "points" for "lines" and all the points came up exactly where they need to be, but how can I make it work with "lines"?
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