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R Under development (unstable) (2019-11-17 r77430) -- "Unsuffered Consequences"
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Copyright (C) 2019 The R Foundation for Statistical Computing
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Platform: x86_64-pc-linux-gnu (64-bit)
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R is free software and comes with ABSOLUTELY NO WARRANTY.
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You are welcome to redistribute it under certain conditions.
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Type 'license()' or 'licence()' for distribution details.
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R is a collaborative project with many contributors.
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Type 'contributors()' for more information and
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'citation()' on how to cite R or R packages in publications.
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Type 'demo()' for some demos, 'help()' for on-line help, or
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'help.start()' for an HTML browser interface to help.
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Type 'q()' to quit R.
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> #### Testing  UseMethod() and even more NextMethod()
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> #### --------------------
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> #### i.e.,  S3 methods *only*. For S4, see  reg-S4.R
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> ##                                          ~~~~~~~~
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>
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> ###-- Group methods
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>
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> ## previous versions used print() and hit an auto-printing bug.
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>
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> ### Arithmetic "Ops" :
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> ">.bar" <- function(...) {cat("using >.bar\n"); FALSE}
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> ">.foo" <- function(...) {cat("using >.foo\n"); TRUE}
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> Ops.foo <- function(...) {
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+     cat("using Ops.foo\n")
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+     NextMethod()
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+ }
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> Ops.bar <- function(...) {
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+     cat("using Ops.bar\n")
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+     TRUE
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+ }
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>
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> x <- 2:4 ; class(x) <- c("foo", "bar")
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> y <- 4:2 ; class(y) <- c("bar", "foo")
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>
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> ## The next 4 give a warning each about incompatible methods:
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> x > y
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[1] FALSE FALSE  TRUE
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Warning message:
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Incompatible methods (">.foo", ">.bar") for ">"
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> y < x # should be the same (warning msg not, however)
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[1] FALSE FALSE  TRUE
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Warning message:
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Incompatible methods ("Ops.bar", "Ops.foo") for "<"
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> x == y
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[1] FALSE  TRUE FALSE
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Warning message:
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Incompatible methods ("Ops.foo", "Ops.bar") for "=="
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> x <= y
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[1]  TRUE  TRUE FALSE
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Warning message:
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Incompatible methods ("Ops.foo", "Ops.bar") for "<="
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>
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> x > 3 ##[1] ">.foo"
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using >.foo
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[1] TRUE
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>
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> rm(list=">.foo")
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> x > 3 #-> "Ops.foo" and ">.bar"
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using Ops.foo
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using >.bar
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[1] FALSE
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>
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>
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>
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> ### ------------  was ./mode-methods.R till R ver. 1.0.x ----------------
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>
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> ###-- Using Method Dispatch on "mode" etc :
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> ## Tests S3 dispatch with the class attr forced to be data.class
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> ## Not very relevant when S4 methods are around, but kept for historical interest
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> abc <- function(x, ...) {
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+     cat("abc: Before dispatching; x has class `", class(x), "':", sep="")
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+     str(x)
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+     UseMethod("abc", x) ## UseMethod("abc") (as in S) fails
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+ }
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>
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> abc.default <- function(x, ...) sys.call()
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>
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> "abc.(" <- function(x)
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+     cat("'(' method of abc:", deparse(sys.call(sys.parent())),"\n")
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> abc.expression <- function(x)
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+     cat("'expression' method of abc:", deparse(sys.call(sys.parent())),"\n")
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>
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> abc(1)
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abc: Before dispatching; x has class `numeric': num 1
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abc.default(1)
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> e0 <- expression((x))
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> e1 <- expression(sin(x))
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> abc(e0)
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abc: Before dispatching; x has class `expression':  expression((x))
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'expression' method of abc: abc.expression(e0)
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> abc(e1)
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abc: Before dispatching; x has class `expression':  expression(sin(x))
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'expression' method of abc: abc.expression(e1)
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> abc(e0[[1]])
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abc: Before dispatching; x has class `(': language, mode "(": (x)
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'(' method of abc: `abc.(`(e0[[1]])
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> abc(e1[[1]])
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abc: Before dispatching; x has class `call': language sin(x)
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abc.default(e1[[1]])
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>