title: sum function in R giving non-credible results
body: <p>I have the following numeric vector taken from a basic data.frame.
  I want to do a simple sum and it gives me weird results.</p>
  <pre><code>x 
  [1] -1.06 -5.36  4.74 -5.66  1.64 -2.86  8.04  2.54 -1.36 -0.66
  
  sum(x)
  [1] -7.105427e-15
  </code></pre>
  <p>I have tried using cumsum to see if the problem comes from one of the values specifically. I guess the problem is with the last value but I don't understand why.</p>
  <pre><code>cumsum(x)
  1] -1.060000e+00 -6.420000e+00 -1.680000e+00 -7.340000e+00 -5.700000e+00
   [6] -8.560000e+00 -5.200000e-01  2.020000e+00  6.600000e-01 -7.105427e-15
  </code></pre>
  <p>I have restarted the R session. I'm using version R version 3.6.3 (2020-02-29).
  And i'm using these libraries to read and reshape the data.</p>
  <pre><code>library(readxl)
  library(dplyr)
  library(tidyr)
  </code></pre>
  <p>Is there a known thing to look for when using specific libraries or a way of showing certain numbers in a particular way?
  Thanks in advance.</p>