R的read.table中的“和”之间有什么区别？

Question

Here is my simple text (named test):

  name      sex     age  height  
1 x1        F       18   162
2 x2        M       19   170
3 x3        M       21   178
4 x4        F       22   166
5 x5        F       23   165

>read.table('test', sep='') 

It's ok.

>read.table('test', sep=' ')  

Error in scan(file, what, nmax, sep, dec, quote, skip, nlines, na.strings,  :   
  line 1 did not have 20 elements  

I want to know why.

What is the difference between '' and ' ' in read.table of R? Please tell me the reason.

Answer 1

As explained in the documentation, the default value of '' means "any amount of whitespace" whereas your second choice ' ' means precisely one space which is in fact very different.

The wording (in help(read.table) ) is not ideal but gets the job done:

  sep: the field separator character. Values on each line of the file are separated by this character. If 'sep = ""' (the default for 'read.table') the separator is 'white space', that is one or more spaces, tabs, newlines or carriage returns. 

You want the default value, unless you know you have, say, a comma-delimited csv file.