[R] lattice xyplot with cumsum() function inside

[Ivan Krylov]

В Sat, 28 Sep 2024 13:34:22 +0000
Naresh Gurbuxani <naresh_gurbuxani using hotmail.com> пишет:

> mydt[, lapply(.SD, sum), by = .(xgroup), .SDcols = c("x")]
> #   xgroup        x
> #   <char>    <num>
> #1:      A 26.00455
> #2:      B 71.55405
> 
> #For xgroup = "B", line starts at the sum of all previous x values
> including xgroup = "A"
> #Intended result is to separate cumsum(x) for groups "A" and "B"
> mydt[, xyplot(cumsum(x) ~ date, groups = xgroup, type = c("l", "g"))]

> Is this a bug or incorrect use of function?

Thank you very much for providing a reproducible example! Lattice first
evaluates the formula and only then splits the results into groups.
This is a consequence of the design where grouping is handled by the
panel functions such as panel.superpose.

I think you can obtain the desired result by letting data.table group
the rows:

xyplot(
 x ~ date, groups = xgroup, type = c("l", "g"),
 data = mydt[,
  c(list(date=date), lapply(.SD, cumsum)),
  by = xgroup, .SDcols = 'x'
 ]
)

A more idiomatic solution might be:

mydt[,xsum := cumsum(x), by = xgroup]
xyplot(xsum ~ date, groups = xgroup, type = c("l", "g"), data = mydt)

-- 
Best regards,
Ivan