title: How to set tolerance of expect_equal in testthat when comparing data_frames?
body: <p>I'm having trouble using testthat's tolerance parameter when I check whether two data_frames are equal. Here's a simple example with two data frames:</p>
  
  <pre><code>library(dplyr)
  library(testthat)
  d1 = data_frame(a = c(1, 1),
                  b = c(2, 2))
  d2 = data_frame(a = c(1, 1.00001),
                  b = c(2, 2))
  </code></pre>
  
  <p>When I check for equality, testthat throws an error, even with a sufficiently high tolerance value:</p>
  
  <pre><code>expect_equal(d1, d2,
               tolerance = 0.01)
  
  # Error: d1 not equal to d2
  # Rows in y but not x: 2. Rows with difference occurences in x and y: 1
  </code></pre>
  
  <p>No error is thrown when I compare the individual vectors:</p>
  
  <pre><code>expect_equal(d1$a, d2$a,
               tolerance = 0.01)
  expect_equal(d1$b, d2$b,
               tolerance = 0.01)
  </code></pre>
  
  <p>Any suggestions? I assume I'm misusing the expect_equal function, but am not sure how to resolve other than running expect_equal on individual columns of the data frame.</p>
  
  <p>Here's the package versions I'm using: </p>
  
  <pre><code>packageVersion("dplyr")
  # [1] ‘0.4.3’
  packageVersion("testthat")
  # [1] ‘0.11.0’
  </code></pre>