title: Avoid that space in column name is replaced with period (".") when using read.csv()
body: <p>I am using R to do some data pre-processing, and here is the problem that I am faced with: I input the data using <code>read.csv(filename,header=TRUE)</code>, and then the space in variable names became ".", for example, a variable named <em>Full Code</em> became <em>Full.Code</em> in the generated dataframe. After the processing, I use <code>write.xlsx(filename)</code> to export the results, while the variable names are changed. How to address this problem?</p>
  
  <p>Besides, in the output <em>.xlsx</em> file, the first column become indices(i.e., 1 to N), which is not what I am expecting.</p>