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R : Copyright 2003, The R Development Core Team
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Version 1.8.0 Under development (unstable) (2003-07-02)
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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.
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Type `demo()' for some demos, `help()' for on-line help, or
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`help.start()' for a 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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>
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> ###-- Group methods
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>
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> ### Arithmetic "Ops" :
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> ">.bar" <- function(...) print(">.bar")
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> ">.foo" <- function(...) print(">.foo")
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> Ops.foo <- function(...) {
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+     print("Ops.foo")
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+     NextMethod()
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+ }
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> Ops.bar <- function(...)
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+     print("Ops.bar")
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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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[1] ">.foo"
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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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[1] "Ops.foo"
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[1] ">.bar"
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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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>