title: How to fix the warning "label `' multiply defined"
body: <p>I am running an lm regression in r, where there are categorical variables and numerical variables. I am usig knitr to compile the Rnw file to make a pdf. I use texreg to make latex regression tables. But when I do the compiling, it reported that lots of lines "Label `' multiply defined". 
  Is it a must that we should assign label to each variable in the regression? But for those factor variables, I tried to assign label, like label(data$var) &lt;- "name", then the warning is "label" command cannot be applied to the class of factor. Now I am really confused. 
  Can anyone help me with this?</p>