title: Concatenate columns if they don't contain a zero
body: <p>Im trying to concatenate 4 <a href="https://i.stack.imgur.com/JWwbP.png" rel="nofollow noreferrer">Columns</a> into a single column named &quot;tags&quot; for later use of multilabel classification. I would like to concate the columns in a way that gives a an output only pasting columns that are not zero and thereto seperate them with a comma.
  An example would be that the cell in last row would be {1,2} instead of {1,2,0,0}</p>
  <p>I currently have no code that works as needed and haven't been able to find something on the internet. Do you guys have a tip to do this?</p>
  <p>Current code:</p>
  <pre><code>df$TV[df$TV==1] = '1'
  df$Internet[df$Internet ==1] = '2'
  df$Mobil[df$Mobil==1] = '3'
  df$Fastnet[df$Fastnet==1] = '4'
  df$tags = paste(df$TV,df$Internet,df$Mobil,df$Fastnet,  sep=&quot;,&quot;)
  </code></pre>