title: R remove numbers in data frame entries containing only numbers
body: <p>I am reading in a data frame from an online csv file, but the person who create the file has accidentally entered some numbers into column which should just be city names. Sample for <code>cities.data</code> table.</p>
  
  <pre><code>City        Population   Foo   Bar
  Seattle     10           foo1  bar1
  98125       20           foo2  bar2
  Kent 98042  30           foo3  bar3
  98042 Kent  30           foo4  bar4
  </code></pre>
  
  <p>Desired output after removing rows with only numbers in the city column:</p>
  
  <pre><code>City        Population   Foo   Bar
  Seattle     10           foo1  bar1
  Kent 98042  30           foo3  bar2
  98042 Kent  30           foo4  bar4
  </code></pre>
  
  <p>I want to remove the rows with ONLY numbers in the city column. Kent 98042 and 98042 Kent are both okay since it contains the city name, but since 98125 is not a city I remove that row. </p>
  
  <p>I can't use <code>is.numeric</code> because the number is being read as a string in the csv file. I tried using regex,</p>
  
  <pre><code>cities.data &lt;- cities.data[which(grepl("[0-9]+", cities.data) == FALSE)]
  </code></pre>
  
  <p>But this deletes rows with any numbers rather than just the one containing only numbers, e.g.</p>
  
  <pre><code>City        Population   Foo   Bar
  Seattle     10           foo1  bar1
  </code></pre>
  
  <p><code>"Kent 98042"</code> was deleted even though I wanted to keep that row. 
  Suggestions? Please and thanks!</p>