How does spplot really work?

[Pacharapol Withayasakpunt]

E.cutoff <- c(70, 100, 120, 140, 180)
cat.E <- cut(
    unlist(data.suicides$E),
    breaks=E.cutoff,
    include.lowest=TRUE
)
maps.cat.E <- data.frame(ID=data.suicides$ID, cat.E=cat.E)
attr(london.gen, "data") <- merge(
    attr(london.gen, "data"),
    maps.cat.E,
    by="ID"
)
spplot(
    obj=london.gen,
    zcol="cat.E",
    main=list(label="Expected case", cex=1),
    col.regions=gray(seq(0.9, 0.1, length=4))
)

As I can see, attr(london.gen, "data") is updated prior to running spplot, but why?

[Saravalee Suphakarn]

You may need to attribute london.gen to the data.boroughs before merge, as command below.

E.cutoff <- c(70, 100, 120, 140, 180)
cat.E <- cut(unlist(data.suicides$E), breaks = E.cutoff, include.lowest = T)
maps.cat.E <- data.frame(ID=data.suicides$ID, cat.E=cat.E)
data.boroughs <- attr(london.gen, “data”)
attr(london.gen, “data”) <- merge(data.boroughs, maps.cat.E, by=”ID”)
spplot(obj = london.gen, zcol = “cat.E”, main=list(label=”Expected case”, cex=1), col.regions=gray(seq(0.9,0.1,length=4)))

Hope it can solve your problem.

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