title: Define one column only when reading in a list of csv files?
body: <p>I'm reading in a list of files and combining into a single df with:</p>
  <pre><code>fi &lt;- list.files(path = 'data', pattern = '*.csv', full.names = T) %&gt;%  
    map_df(~read_csv(paste0(.)))
  </code></pre>
  <p>But this is hitting an error:</p>
  <blockquote>
  <p>Error: Can't combine <code>App ID</code> &lt;character&gt; and <code>App ID</code> &lt;double&gt;. .</p>
  </blockquote>
  <p>Within the directory in question there are many files to read in and combine. I'd like to know if it's possible to define the column type for the problem field, <code>App ID</code> while reading in like this? E.g. <code>map_df(~read_csv(paste0(.), cols(</code>App ID = CHR<code>))</code></p>