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rr-grid

element replacement in grid unit vector

I've been baffled by this a few times already, so here's a made-up question for others who might stumble upon the same problem.

Consider this grid unit vector,

a = unit(1:3, c("cm", "in", "npc"))

I want to replace some elements with new values. The natural approach would be,

a[1] = unit(2,"pt")
a
# [1] 2cm  2in  3npc

Something went wrong: only the numeric value was changed, not the unit. Why? What to do?

Edit: As pointed out in one answer below, such units are just numeric vectors with attributes. However, their offsprings unit.arithmetic and unit.list should also be considered solution to be fully general (e.g to use in adjusting panel sizes of ggplot objects). Consider this unit vector,

(b = a + unit(1, "npc"))
# [1] 1cm+1npc  2in+1npc  3npc+1npc
# [1] "unit.arithmetic" "unit"

Now replacing a specific element is more tricky, since they're not atomic anymore.

Solution

  • grid now has a [<-.unit method.