 <p>You can change the raw data from "&lt;0" to "-1" before you tabulate it with:</p> <pre><code>credit_arff$checking_status[ credit_arff$checking_status=="&lt;0" ] &lt;- "-1" </code></pre> <p>Or you can tabulate it first and then get the headings with</p> <pre><code>rownames(table(credit_arff$checking_status) </code></pre> <p>...and change it there if you want. The limiting factor is that the vector of data, or the vector of rownames, will not contain a mix of numeric and character data. Even if you omit the doublequotes around "-1" from the code above, the data will change to "-1". Whether that's acceptable depends what you're doing with the numbers next. Or will you be changing all the other contents to numeric as well?</p>