[R] Need help figuring out sapply (and similar functions) with multiple parameter user defined function

[PIKAL Petr]

Hi

The warning is due to fact that "if" takes only single scalar value not an entire vector.

Maybe you shall explain more clearly what result do you expect.

I bet that there is vectorised solution to your problem but I am lost in your ifs and cannot follow what shall be the output.

Please use 

dput(head(df))

when showing input data and clearly describe intended result.

Regards
Petr


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Walter Anderson
> Sent: Friday, December 06, 2013 4:44 PM
> To: r-help at r-project.org
> Subject: [R] Need help figuring out sapply (and similar functions) with
> multiple parameter user defined function
> 
> I am having trouble understanding how to use sapply (or similar
> functions) with a user defined function with multiple parameters.
> 
> I have the following functions defined
> 
>     q1.ans <- function(x)
>     {
>        retVal = 0
>        if (x == 1) {
>          retVal = 1
>        } else if (x ==2) {
>          retVal = 2
>        }
>        return (retVal)
>     }
>     q2.ans <- function(x)
>     {
>        retVal = 0
>        if (x == 1) {
>          retVal = 1
>        } else if (x ==2) {
>          retVal = 3
>        }
>        return (retVal)
>     }
>     q3.ans <- function(x)
>     {
>        retVal = 0
>        if (x == 1) {
>          retVal = 2
>        } else if (x ==2) {
>          retVal = 3
>        }
>        return (retVal)
>     }
> 
>     evaluate.questions <- function(q.1,q.2,q.3)
>     {
>        a <- q1.ans(q.1)
>        b <- q2.ans(q.2)
>        c <- q3.ans(q.3)
>        retVal = 0   # Set default value to be no preference
>        # The following code only implements those values from the state
>     machine that show a preference (ID's 5,9,11,13-15,17-18,21,23-27)
>        if (a == 0) {
>          if (b == 1) {
>            if (c == 1) {
>              retVal = 1  # State machine ID 5
>            }
>          } else if (b == 2) {
>            if (c == 2) {
>              retVal = 2  # State machine ID 9
>            }
>          }
>        } else if (a == 1) {
>          if (b == 0) {
>            if (c == 1) {
>              retVal = 1  # State machine ID 11
>            }
>          } else if (b == 1) {
>            retVal = 1    # State machine ID's 13-15, value of C doesn't
>     matter
>          } else if (b == 2) {
>            if (c == 1) {
>              retVal = 1  # State machine ID 17
>            } else if (c == 2) {
>              retVal = 2  # State machine ID 18
>            }
>          }
>        } else if (a == 2) {
>          if (b == 0) {
>            if (c == 2) {
>              retVal = 2  # State machine ID 21
>            }
>          } else if (b == 1) {
>            if (c == 1) {
>              retVal = 1  # State machine ID 23
>            } else if (c == 2) {
>              retVal = 2  # State machine ID 24
>            }
>          } else if (b == 2) {
>            retVal = 2    # State machine ID's 25-27, value of C doesn't
>     matter
>          }
>        }
>        return (retVal)
>     }
> 
> And a data set that looks like this:
> 
>     ID,Q1,Q2,Q3
>     1,2,2,2
>     2,2,1,1
>     3,1,1,1
>     4,1,2,2
>     5,2,2,1
>     6,1,2,1
>     ...
> 
> 
> I have been researching and it appears that I should be using the
> sapply function to apply the evaluate.question function above to each
> row in the data frame like this
> 
> preferences <- sapply(df, evaluate.questions, function(x,y,z)
> evaluate.questions(df['Q1'],df['Q2'],df['Q3']))
> 
> Unfortunately this doesn't work and the problem appears that the sapply
> function is not feeding the parameters to the evaluate.questions
> function as I expect.  Can someone provide some guidance on what I am
> doing wrong?
> 
> This is the error message I am getting:
> 
> Error in x --1 :
>    Comparison (1) is possible only for atomic and list types In
> addition: warning messages:
> In if (x == 1) { :
>    the condition has length > 1 and only the first element will be used
> 
> 	[[alternative HTML version deleted]]
> 
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