How to read in numbers with a comma as decimal separator?

When you check ?read.table you will probably find all the answer that you need.

There are two issues with (continental) European csv files:

1. What does the c in csv stand for? For standard csv this is a ,, for European csv this is a ;
sep is the corresponding argument in read.table
2. What is the character for the decimal point? For standard csv this is a ., for European csv this is a ,
dec is the corresponding argument in read.table

To read standard csv use read.csv, to read European csv use read.csv2. These two functions are just wrappers to read.table that set the appropriate arguments.

If your file does not follow either of these standards set the arguments manually.

From ?read.table:

dec     the character used in the file for decimal points.

And yes, you can use that for read.csv as well. (to me: no stupid, you cannot!)

Alternatively, you can also use

read.csv2

which assumes a "," decimal separator and a ";" for column separators.