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Data Checking

5 messages · Ko-Kang Kevin Wang, Uwe Ligges, Göran Broström +2 more

Ko-Kang Kevin Wang
# 
Hi,

This is a simple question with if elseif....however I am having trouble
constructing the solution for some reason.

Suppose I have a data set with 3 variables, a, b and c say.  Let's say c
is the sum of a and b.  So:
  a  b  c
  1  2  3
  2  3  5
  3  4  7
  .  .  .
  .  .  .
  .  .  .

Suppose that I know there have been some data entry errors and I want to
check if ALL values in c is really the sum of a and b, and if not, print
out the whole line (i.e. all values of a, b and c in that row).

Any help on how I can write this if elseif block will be apprecaited!

Ko-Kang

------------------------------------------------------------------------------
Ko-Kang Kevin Wang
Postgraduate PGDipSci Student
Department of Statistics
University of Auckland
New Zealand

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Uwe Ligges
#
Ko-Kang Kevin Wang wrote:
Assume your "data set" is a data.frame():

 X <- data.frame(a=1:5, b=2:6, ce=c(3,5,7,6,11)) 
 # Let's call it a, b, ce --- c already is a function
 # Now get the rows with errors:
 X[X$a + X$b != X$ce, ]


So you neither need the construct
  if(condition){
	statement
  }
  else{
	statement2
  }

nor
  elseif(condition, statement1, statement2)

Uwe Ligges
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Göran Broström
#
On Sun, 24 Mar 2002, Ko-Kang Kevin Wang wrote:

            

      
      
      
    

        
Try subsetting:

            

      
      
      
    

        
is what you want. You should consider whether you want to test exact or
approximate equality, though.

G?ran

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      ggrothendieck@yifan.net
    

    

      
      #
    

  


  

      
d <- data.frame( a  = 1:3, b = 2:4, c=c(3,5,9) )    # last row wrong
  subset(d, a+b!=c )

        
On 24 Mar 2002 at 22:41, Ko-Kang Kevin Wang wrote:

        

            

      
      
      
    

        
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      Ott Toomet
    

    

      
      #
    

  


  

      
On Sun, 24 Mar 2002, Uwe Ligges wrote:

        

        
|Ko-Kang Kevin Wang wrote:

        
|> 
  |> Hi,
  |> 
  |> This is a simple question with if elseif....however I am having trouble
  |> constructing the solution for some reason.
  |> 
  |> Suppose I have a data set with 3 variables, a, b and c say.  Let's say c
  |> is the sum of a and b.  So:
  |>   a  b  c
  |>   1  2  3
  |>   2  3  5
  |>   3  4  7
  |>   .  .  .
  |>   .  .  .
  |>   .  .  .
  |> 
  |> Suppose that I know there have been some data entry errors and I want to
  |> check if ALL values in c is really the sum of a and b, and if not, print
  |> out the whole line (i.e. all values of a, b and c in that row).
  |> 
  |> Any help on how I can write this if elseif block will be apprecaited!
  |
  |Assume your "data set" is a data.frame():
  |
  | X <- data.frame(a=1:5, b=2:6, ce=c(3,5,7,6,11)) 
  | # Let's call it a, b, ce --- c already is a function
  | # Now get the rows with errors:
  | X[X$a + X$b != X$ce, ]
  |

I do recommend not to use == or != to test equality.  Operators == or != are usable
== _only_ for integers.  Generally, on digital computers you can never know
when two real numbers are equal.  Here is a simle example (R 1.4.0, P-II,
linux):

            

      
      
      
    

        
[1] 3

            

      
      
      
    

        
[1] TRUE

            

      
      
      
    

        
[1] 3.3

            

      
      
      
    

        
[1] FALSE

So, using Uwe's example, you should write something like

tolerance= .Machine$double.eps ^ 0.5

            

      
      
      
    

        
a b ce
4 4 5  6


Regards,

Ott Toomet


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