title: maps - deleting data
body: <p>How does one delete data from a map in Go? For example, having</p>
  
  <pre><code>m := map[string]string{ "key1":"val1", "key2":"val2" };
  </code></pre>
  
  <p>I want to make m drop the "key1" without copying the entire map by iterating over its keys (which could get big in some uses). Is it enough to assign a nil value to "key1", or will that still keep the key in the map structure with an assigned value of nil? That is, if I later iterate over the keys of the map, will "key1" appear?</p>