 <p>This is typically what I do when I want to convert many columns in a data.frame to a different data type:</p> <pre><code>convNames &lt;- c("NY", "CHI", "LA", "ATL", "MIA") for(name in convNames) { city1[, name] &lt;- as.numeric(as.character((city1[, name])) } </code></pre> <p>It's a nice two lines and you just have to add the names of whatever columns you want to coerce to the convNames vector to add a new column to the coercing loop below.</p> <p>EDIT: Do to a factor issue, do the lapply method above.</p>