Implement near.

Fixes #1607.
tidyverse · Mar 7, 2016 · 0ebdf60 · 0ebdf60
1 parent 97e656d
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diff --git a/DESCRIPTION b/DESCRIPTION
@@ -76,6 +76,7 @@ Collate:
     'lead-lag.R'
     'location.R'
     'manip.r'
+    'near.R'
     'nth-value.R'
     'order-by.R'
     'over.R'

diff --git a/NAMESPACE b/NAMESPACE
@@ -410,6 +410,7 @@ export(mutate_each_q)
 export(n)
 export(n_distinct)
 export(n_groups)
+export(near)
 export(nth)
 export(ntile)
 export(nycflights13_postgres)

diff --git a/NEWS.md b/NEWS.md
@@ -1,5 +1,7 @@
 # dplyr 0.4.3.9000
 
+* new `near(x, y)` is a helper for `abs(x, y) < tol` (#1607).
+
 * new `as_data_frame.tbl_cube()` (#1563, @krlmlr).
 
 * new parameters `indexes` and `unique_indexes` to `compute()` (#1499, @krlmlr).

diff --git a/R/near.R b/R/near.R
@@ -0,0 +1,15 @@
+#' Compare two numeric vectors.
+#'
+#' This is a safe way of comparing if two vectors of floating point numbers
+#' are (pairwise) equal.  This is safer than using \code{==}, because it has
+#' a built in tolerance
+#'
+#' @param x,y Numeric vectors to compare
+#' @param tol Tolerance of comparison.
+#' @export
+#' @examples
+#' sqrt(2) ^ 2 == 2
+#' near(sqrt(2) ^ 2, 2)
+near <- function(x, y, tol = .Machine$double.eps ^ 0.5) {
+  abs(x - y) < tol
+}
diff --git a/man/near.Rd b/man/near.Rd
diff --git a/tests/testthat/context-near.R b/tests/testthat/context-near.R
@@ -0,0 +1,5 @@
+context("near")
+
+test_that("near accepts nearby fp values", {
+  expect_true(near(sqrt(2) ^ 2, 2))
+})