108 lines
2.5 KiB
R
108 lines
2.5 KiB
R
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## ---- echo = FALSE-------------------------------------------------------
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knitr::opts_chunk$set(collapse = TRUE, comment = "#>")
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rownames(mtcars) <- NULL
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## ------------------------------------------------------------------------
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library(lazyeval)
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f <- function(x = a - b) {
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lazy(x)
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}
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f()
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f(a + b)
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## ------------------------------------------------------------------------
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a <- 10
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b <- 1
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lazy_eval(f())
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lazy_eval(f(a + b))
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## ------------------------------------------------------------------------
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lazy_eval(f(), list(a = 1))
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## ------------------------------------------------------------------------
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lazy_eval(~ a + b)
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h <- function(i) {
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~ 10 + i
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}
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lazy_eval(h(1))
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## ------------------------------------------------------------------------
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subset2_ <- function(df, condition) {
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r <- lazy_eval(condition, df)
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r <- r & !is.na(r)
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df[r, , drop = FALSE]
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}
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subset2_(mtcars, lazy(mpg > 31))
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## ------------------------------------------------------------------------
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subset2_(mtcars, ~mpg > 31)
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subset2_(mtcars, quote(mpg > 31))
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subset2_(mtcars, "mpg > 31")
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## ------------------------------------------------------------------------
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subset2 <- function(df, condition) {
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subset2_(df, lazy(condition))
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}
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subset2(mtcars, mpg > 31)
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## ------------------------------------------------------------------------
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above_threshold <- function(df, var, threshold) {
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cond <- interp(~ var > x, var = lazy(var), x = threshold)
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subset2_(df, cond)
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}
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above_threshold(mtcars, mpg, 31)
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## ------------------------------------------------------------------------
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x <- 31
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f1 <- function(...) {
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x <- 30
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subset(mtcars, ...)
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}
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# Uses 30 instead of 31
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f1(mpg > x)
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f2 <- function(...) {
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x <- 30
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subset2(mtcars, ...)
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}
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# Correctly uses 31
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f2(mpg > x)
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## ---- eval = FALSE-------------------------------------------------------
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# x <- 31
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# g1 <- function(comp) {
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# x <- 30
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# subset(mtcars, comp)
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# }
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# g1(mpg > x)
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# #> Error: object 'mpg' not found
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## ------------------------------------------------------------------------
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g2 <- function(comp) {
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x <- 30
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subset2(mtcars, comp)
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}
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g2(mpg > x)
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## ------------------------------------------------------------------------
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library(lazyeval)
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f1 <- function(x) lazy(x)
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g1 <- function(y) f1(y)
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g1(a + b)
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## ------------------------------------------------------------------------
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f2 <- function(x) lazy(x, .follow_symbols = FALSE)
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g2 <- function(y) f2(y)
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g2(a + b)
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## ------------------------------------------------------------------------
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a <- 10
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b <- 1
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lazy_eval(g1(a + b))
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lazy_eval(g2(a + b))
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