Changing factors to Integers without changing the order of the data

Question

I have following data and trying change CCG and Pract to numbers so I can use stan or Winbugs...when I try to change it seems its changing the order of the data.. I want to change CCG and Pract to numbers without changing the order of the data...I tried hard but I couldn't do it. I am struggling with this basic issue than writing Bugs codes....please help..

I have the following data

  CCG  pract  Deno Numer Points  Excep 
1 01C N81049   49    46      4       4           
2 01C N81022   28    26      4      23          
3 01C N81632   66    64      4       4          
4 01C N81069   15    14      4       3           
5 01C N81062   98    89      4       9          
6 01C N81033   31    28      4       9

I tried to change to integer using as.integer() and I am getting I am getting..

  CCG pract Deno Numer Points Excep
1  20  6621  160   144    41    36       
2  20  6594  130   117    41    18       
3  20  6698  179   164    41    36       
4  20  6640   57    46    41    25       
5  20  6633  214   191    41    62       
6  20  6605  137   119    41    62

By checking Deno and Numer it is clear the order of the data has been changed...Why CCG is not starting from 1?

I want

   CCG  pract  Deno Numer   Points Excep 
1 01C N81049   49    46      4         4           
2 01C N81022   28    26      4        23          
3 01C N81632   66    64      4         4          
4 01C N81069   15    14      4         3           
5 01C N81062   98    89      4         9          
6 01C N81033   31    28      4         9

change to something like this

  CCG  pract     Deno Numer    Points Excep 
1    1    1      49    46        4       4           
2    1    1      28    26        4      23          
3    1    1      66    64        4       4          
4    1    1      15    14        4       3          
5    1    1      98    89        4       9          
6    1    1      31    28        4       9

Please help me..

Relevel the factors so they're in the order they appear (use `unique` to get that), then convert to integer. — Ari B. Friedman, Apr 02 '14 at 12:41
possible duplicate of [Convert factor to integer](http://stackoverflow.com/questions/4798343/convert-factor-to-integer) — Aaron left Stack Overflow, Apr 02 '14 at 13:05

score 2 · Answer 1 · answered Apr 02 '14 at 12:51

2

In R, factors are internally represented as integers, linking to a table of the factor levels. AFAIK, these internal integers are assigned based on a lexicographic order of the factor levels, so 57 gets a higher code than 238.

as.integer() will extract this internal integer coding. As you found out, this is not very useful. (I honestly don't understand why R does this when applying as.integer() to factors that have integers as factor levels.)

Solution: first convert to character, then to integer. as.integer(as.character(Deno))

answered Apr 02 '14 at 12:51

Stephan Kolassa

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Another option to do this is `as.numeric(levels(f))[f]`; this is preferred by the help page, but admittedly is not as clear to understand. – Aaron left Stack Overflow Apr 02 '14 at 13:04
when I try as.numeric(as.character(CCG)) I am getting a warning message: NAs introduced by coercion. – Vera Apr 03 '14 at 20:34
@Vera: CCG cannot be interpreted as an integer, here my solution won't work. Have you tried Aaron's? – Stephan Kolassa Apr 03 '14 at 20:58

Changing factors to Integers without changing the order of the data

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