What does negative index mean in a data frame? : <p>Recently I read a R statement somewhere, which said:</p>

<pre><code>mtcars[-1]
</code></pre>

<p>What does -1 imply here? I do understand the following statement:</p>

<pre><code>mtcars[1]
</code></pre>

<p>which means select the first column from the data frame, but I just could not infer the negative sign in the index?</p>
