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How to write generic function with two inputs?

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11

1

I am a newbee in programming, and I run into an issue with R about generic function: how to write it when there are multiple inputs?

For an easy example, for dataset and function

z <- c(2,3,4,5,8)
calc.simp <- function(a,x)a*x+8
# Test the function:
calc.simp(x=z,a=3)
[1] 14 17 20 23 32

Now I change the class of z:
class(z) <- 'simp'
How should I write the generic function 'calc' as there are two inputs?
My attempts and errors are below:

calc <- function(x) UseMethod('calc',x)
calc(x=z)
Error in calc.simp(x = z) : argument "a" is missing, with no default

And

calc <- function(x,y) UseMethod('calc',x,y)
Error in UseMethod("calc", x, y) : unused argument (y)

My confusion might be a fundamental one as I am just a beginner. Please help! Thank you very much!

r generic-programming

share|improve this question

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What do you expect to be returned from calc(x=z)? You aren't giving your function a value for a and your function depends on it. Also you can let your generic function know there may be other argumets with calc <- function(x, ...) UseMethod('calc',x)
  
  – MrFlick
  Apr 3 at 19:45
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  What do you want your function to do? Your first function (calc.simp) still works even after changing the class of z.
  
  – Luis
  Apr 3 at 19:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MrFlick I simply want to test whether my generic function can work! It helps me understand the dispatch mechanism better. The 'function(x,...)' works perfectly for my question. Thank you so much! :)
  
  – Branda Newbee
  Apr 3 at 19:58
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  question is about dispatching? didn't see this keyword anywhere on this page, hence adding it here.
  
  – chinsoon12
  Apr 4 at 0:24
  

  
  
  
  

add a comment | 

11

1

I am a newbee in programming, and I run into an issue with R about generic function: how to write it when there are multiple inputs?

For an easy example, for dataset and function

z <- c(2,3,4,5,8)
calc.simp <- function(a,x)a*x+8
# Test the function:
calc.simp(x=z,a=3)
[1] 14 17 20 23 32

Now I change the class of z:
class(z) <- 'simp'
How should I write the generic function 'calc' as there are two inputs?
My attempts and errors are below:

calc <- function(x) UseMethod('calc',x)
calc(x=z)
Error in calc.simp(x = z) : argument "a" is missing, with no default

And

calc <- function(x,y) UseMethod('calc',x,y)
Error in UseMethod("calc", x, y) : unused argument (y)

My confusion might be a fundamental one as I am just a beginner. Please help! Thank you very much!

r generic-programming

share|improve this question

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What do you expect to be returned from calc(x=z)? You aren't giving your function a value for a and your function depends on it. Also you can let your generic function know there may be other argumets with calc <- function(x, ...) UseMethod('calc',x)
  
  – MrFlick
  Apr 3 at 19:45
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  What do you want your function to do? Your first function (calc.simp) still works even after changing the class of z.
  
  – Luis
  Apr 3 at 19:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MrFlick I simply want to test whether my generic function can work! It helps me understand the dispatch mechanism better. The 'function(x,...)' works perfectly for my question. Thank you so much! :)
  
  – Branda Newbee
  Apr 3 at 19:58
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  question is about dispatching? didn't see this keyword anywhere on this page, hence adding it here.
  
  – chinsoon12
  Apr 4 at 0:24
  

  
  
  
  

add a comment | 

I am a newbee in programming, and I run into an issue with R about generic function: how to write it when there are multiple inputs?

For an easy example, for dataset and function

z <- c(2,3,4,5,8)
calc.simp <- function(a,x)a*x+8
# Test the function:
calc.simp(x=z,a=3)
[1] 14 17 20 23 32

Now I change the class of z:
class(z) <- 'simp'
How should I write the generic function 'calc' as there are two inputs?
My attempts and errors are below:

calc <- function(x) UseMethod('calc',x)
calc(x=z)
Error in calc.simp(x = z) : argument "a" is missing, with no default

And

calc <- function(x,y) UseMethod('calc',x,y)
Error in UseMethod("calc", x, y) : unused argument (y)

My confusion might be a fundamental one as I am just a beginner. Please help! Thank you very much!

r generic-programming

share|improve this question

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

z <- c(2,3,4,5,8)
calc.simp <- function(a,x)a*x+8
# Test the function:
calc.simp(x=z,a=3)
[1] 14 17 20 23 32

calc <- function(x) UseMethod('calc',x)
calc(x=z)
Error in calc.simp(x = z) : argument "a" is missing, with no default

calc <- function(x,y) UseMethod('calc',x,y)
Error in UseMethod("calc", x, y) : unused argument (y)

share|improve this question

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

New contributor

Branda Newbee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked Apr 3 at 19:36

Branda NewbeeBranda Newbee

584

1 Answer
1

active

oldest

votes

10

I'd suggest you model your generic function off of the template used by innumerable base R functions as, e.g., mean:

> mean
function (x, ...) 
UseMethod("mean")

In your case, that would translate to the following generic which (if I understand your question correctly) works just fine:

calc <- function(x, ...) UseMethod('calc')

calc.simp <- function(a, x) 
 x <- unclass(x)
 a * x + 8



## Try it out

z <- c(2,3,4,5,8)
class(z) <- "simp"

calc.simp(x = z, 10)
## [1] 28 38 48 58 88

calc(x = z, 10)
## [1] 28 38 48 58 88

share|improve this answer

edited Apr 3 at 20:04

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

add a comment | 

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10

I'd suggest you model your generic function off of the template used by innumerable base R functions as, e.g., mean:

> mean
function (x, ...) 
UseMethod("mean")

In your case, that would translate to the following generic which (if I understand your question correctly) works just fine:

calc <- function(x, ...) UseMethod('calc')

calc.simp <- function(a, x) 
 x <- unclass(x)
 a * x + 8



## Try it out

z <- c(2,3,4,5,8)
class(z) <- "simp"

calc.simp(x = z, 10)
## [1] 28 38 48 58 88

calc(x = z, 10)
## [1] 28 38 48 58 88

share|improve this answer

edited Apr 3 at 20:04

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

add a comment | 

10

I'd suggest you model your generic function off of the template used by innumerable base R functions as, e.g., mean:

> mean
function (x, ...) 
UseMethod("mean")

In your case, that would translate to the following generic which (if I understand your question correctly) works just fine:

calc <- function(x, ...) UseMethod('calc')

calc.simp <- function(a, x) 
 x <- unclass(x)
 a * x + 8



## Try it out

z <- c(2,3,4,5,8)
class(z) <- "simp"

calc.simp(x = z, 10)
## [1] 28 38 48 58 88

calc(x = z, 10)
## [1] 28 38 48 58 88

share|improve this answer

edited Apr 3 at 20:04

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

add a comment | 

I'd suggest you model your generic function off of the template used by innumerable base R functions as, e.g., mean:

> mean
function (x, ...) 
UseMethod("mean")

In your case, that would translate to the following generic which (if I understand your question correctly) works just fine:

calc <- function(x, ...) UseMethod('calc')

calc.simp <- function(a, x) 
 x <- unclass(x)
 a * x + 8



## Try it out

z <- c(2,3,4,5,8)
class(z) <- "simp"

calc.simp(x = z, 10)
## [1] 28 38 48 58 88

calc(x = z, 10)
## [1] 28 38 48 58 88

share|improve this answer

edited Apr 3 at 20:04

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

> mean
function (x, ...) 
UseMethod("mean")

calc <- function(x, ...) UseMethod('calc')

calc.simp <- function(a, x) 
 x <- unclass(x)
 a * x + 8



## Try it out

z <- c(2,3,4,5,8)
class(z) <- "simp"

calc.simp(x = z, 10)
## [1] 28 38 48 58 88

calc(x = z, 10)
## [1] 28 38 48 58 88

share|improve this answer

edited Apr 3 at 20:04

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391

answered Apr 3 at 19:59

Josh O'BrienJosh O'Brien

130k18281391