title: R error "Can't join on ... because of incompatible types"
body: <p>I write code that runs in high throughput production environments expected to handle a variety of input from multiple users.   In this environment, I often need to join (with dplyr) two multi-column dataframes with join columns of mismatched types which produces this error. "Can't join on ... because of incompatible types"</p>
  
  <p>The production code is expected to handle input csvs that are 150+ columns by 0-1000 rows, with 12-20 join columns.  I use read.table for speed, and because the content of the 150 columns can vary, allow type to be inferred by data content.   </p>
  
  <p>It would be great to have a general-purpose function that matches join column types programmatically, making no assumptions about column name or location. </p>