Black and White theme has incorrect legend

[Daniel McKelvey]

Hi everyone,

I wasn't sure if here would be the best place to ask this, but I couldn't find a lattice specific forum, so I thought I would start here. I have been having difficulties with converting plots to the Black and White theme, and I've attached an example plot to show what I mean. I have tried a couple of ways to convert to that theme, and when I do the plots do not match the legend. At first I was wanting to change the legend to match the plot, but I just realized that the plots repeat themselves, so I was actually wondering if there might be a way to change the plots to match the legend perhaps with a trace line through the corresponding shapes.

The plot was created after first running this, which I found elsewhere in this forum:

trellis.device()

trellis.par.set(list(plot.line = list(col = "black")))

Thanks

Daniel McKelvey

[Phil Chalmers]

Interesting question. It looks like lattice doesn't track colour/theme changes very well (this is where I sometimes wish the plots in mirt were written with ggplot2). In your plot you need to modify the output type as well in the legend, which is generated by the auto.key input. Here's an example:

library(mirt)

mod <- mirt(Science, 1)

trellis.device(color=FALSE)

itemplot(mod, 1, type = 'trace', auto.key=list(points=FALSE, lines=TRUE))

I suppose in mirt the legend should be using lines by default anyway rather than points, so perhaps I'll change this internally to ensure everything is kosher where it should be. Cheers.

Phil

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[Daniel McKelvey]

Thanks Phil! That changed the legend to match the lines. One issue is that P1 and P7 lines match in terms of pattern (i.e. they are both solid lines). I think that it should not be too much of an problem since it is pretty clear which is which, but would you be aware of a way to accomplish the reverse of this (i.e. change the trace lines to match the original legend shapes)?

[Phil Chalmers]

Another annoying thing, but I learned a few new things about lattice....so that good. See below:

library(mirt)

mod <- mirt(Science, 1)

theme <- simpleTheme(lty=1:2, col='black')

itemplot(mod, 1, type = 'trace', auto.key=list(points=FALSE, lines=TRUE),

               par.settings=theme)

I figured this out from this thread: http://r.789695.n4.nabble.com/correct-line-types-in-lattice-legends-td893193.html

Phil