[R] apply block of if statements with menu function

[PIKAL Petr]

Hi

> Selection: 1
> Error in if (menu1 == 1) menu1a <- menu(c("1a", "2a", "3a", "4a"),
> graphics = FALSE,  :
>       argument is of length zero
>
> How to correct this error please, for this zero length argument?

Instead of writing functions which you are unable to debug and resolve look what elements of your function returns.

Here is what your first line does

> menu1<-switch(menu(c(1,2,3,4),graphics=FALSE,title="select something"))
select something

1: 1
2: 2
3: 3
4: 4

Selection: 3
> menu1
NULL

Regardless of selection menu1 stays NULL, what is probably not what you want.

> switch(menu(c("List letters", "List LETTERS")) + 1,
>       cat("Nothing done\n"), letters, LETTERS)
>
> why is the result changed if ' + 1,' removed?

Because +1 belongs to switch not to menu. You can translate above to:

open menu with 2 items
select one of those 2 items  or press 0
return 0, 1 or 2 based on your choice
add 1 to returned value to enable **switch** to perform first, second or third item
perform desired item e.g print Nothing done, letters or LETTERS.

Nothing more, nothing less.

so in your case it shall be

menu1 <- menu(c(1,2,3,4),graphics=FALSE,title='select something')
if (menu1 == 1) ...

or
menu1 <- menu1+1

switch (menu1, "Nothing selected",
{do something1},
{do something2},
{do something3},
{do something4})

Regards
Petr

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of rl at openmailbox.org
> Sent: Tuesday, September 16, 2014 11:10 AM
> To: David L Carlson
> Cc: r-help at r-project.org
> Subject: Re: [R] apply block of if statements with menu function
>
> On 2014-09-15 14:22, David L Carlson wrote:
> > I think switch() should work for you here, but it is not clear how
> > much flexibility you are trying to have (different tests based on the
> > first response; different tests based on first, then second response;
> > different tests based on each successive response).
> >
>
> The help page for 'menu' shows:
>
> switch(menu(c("List letters", "List LETTERS")) + 1,
>       cat("Nothing done\n"), letters, LETTERS)
>
> why is the result changed if ' + 1,' removed?
>
> The help page for switch states that "arguments" are required, but this
> conflicts with the syntax for the function 'menu':
>
> > testswitch<-function (testfunctionname) {
> + menu1<-switch(menu(c(1,2,3,4),graphics=FALSE,title='select
> something'))
> + if (menu1==1)
> + menu1a<-menu(c('1a','2a','3a','4a'),graphics=FALSE,title='select
> something else')
> + if (menu1a==1)
> + object1<-seq(1:10)
> + object2<-seq(20:30)
> + menu2a<-menu(c('5a','6a','7a','8a'),graphics=FALSE,title='select
> something else again')
> + if (menu2a==2)
> + object3<-'3y'
> + finalobject<<-object3
> + if (menu1==2)
> + menu2x<-menu(c('5a','15a','20a'),graphics=FALSE,title='select
> something else')
> + if (menu2x==1)
> + object22<-seq(10:100)
> + object22<-seq(2:30)
> + object33<-rnorm(10)
> + menu2y<-menu(c('5a','6a','7a','8a'),graphics=FALSE,title='select
> something else again')
> + if (menu2y==2)
> + object3<-'3y'
> + finalobject<<-object3
> + }
> > testswitch(testfunctionname)
> select something
>
> 1: 1
> 2: 2
> 3: 3
> 4: 4
>
> Selection: 1
> Error in if (menu1 == 1) menu1a <- menu(c("1a", "2a", "3a", "4a"),
> graphics = FALSE,  :
>       argument is of length zero
>
> How to correct this error please, for this zero length argument?
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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