Variable missed in the function

[sbl_bah]

Hello,
At the moment, I try to make the package with several function.

In my function I have 5 variables and I would like to know how I can put a default value of the variable when I omitted to put the variable when I call the function.

toto <- function(format, tab, seuil, taille, varf){ ...} 

For example : when I call my function with only 4 variables

toto <- function(tab, seuil, taille, varf){ ...} 

It miss the format variable.

Have you an idea of how I can put default value on format variable?
I want the default variable to be set to 1 i.e. format = 1

Thanks in advance

[jm_t]

Look at the documentation about functions.

http://adv-r.had.co.nz/Functions.html#function-arguments

You are looking for the section named "Default and missing arguments".

[sbl_bah]

thanks FYI

You will find an example of the function

i <- function(a, b) {
  c(missing(a), missing(b))
}
i()

I want that when I call i(b) the value of the variable a take 1 not TRUE

[jcblum]

That example is demonstrating how to test for missing variables (ones not supplied in the function call) when your function has default values. The very first example in that section is a more basic example of just using default values:

f <- function(a = 1, b = 2) {
  c(a, b)
}
f()

## [1] 1 2

With your example, you could have:

toto <- function(format = 1, tab, seuil, taille, varf){ ...} 

Did you give it a try?

In addition to,the Functions chapter of Advanced R, you might also want to read the chapter on functions in An Introduction to R: https://cran.r-project.org/doc/manuals/r-release/R-intro.html#Writing-your-own-functions

[sbl_bah]

Thanks FYI of the documentation, I will check
The function below is ok

i <- function(a, b) {
  #c(missing(a), missing(b))
  if(missing(a)) {a <-1}
  else a
 x=a+b
}

v<-i(b=2)
v=3
v<-i(a=3,b=2)
v=5

[jcblum]

Sure, but it's more than is necessary:

i <- function(a = 1, b) {
  a + b
}

i(b = 2)
#> [1] 3

i(a = 3, b = 2)
#> [1] 5

^{Created on 2018-12-13 by the reprex package (v0.2.1)}

The purpose of missing() is to let the function tell the difference between: i(b = 2) (the a value is being supplied by the default) and i(a = 3, b = 2) (the a value was supplied by the user, overriding the default), so that the function can do something differently in the two cases. This is pretty specialized — most functions have no need for missing(). It is not necessary if all you want to do is have some default values.

i <- function(a = 1, b) {
  if(missing(a)) message("OK, I'll use the default a = 1")
  a + b
}

i(b = 2)
#> OK, I'll use the default a = 1
#> [1] 3

i(a = 3, b = 2)
#> [1] 5

# Edited to add: Note what happens when we supply
# the same value as the default. This is why `missing()` is
# more powerful than just checking for a particular value

i(a = 1, b = 2)
#> [1] 3

^{Created on 2018-12-13 by the reprex package (v0.2.1)}

[sbl_bah]

I've made some function to create a specific package.
I use missing() in my function because the user can omit some variables and the function can run with default value.
Thanks!