How to build a list with missing values? What is missing, anyway?

This is tangentially related to Hadley's question.

Suppose I'm building a function programmatically; I have assembled an
expression for the body and I know the names of the arguments it wants
to take.

Suppose I have some convenience function such that writing
    make_function(alist(a=, b=), quote(a+b), environment())
is equivalent to writing
    function(a,b) a+b

So how do I make the list that goes in the first argument? Suppose I
start with a character vector of argument names. What I need is a list
with names and quoted values, but the values are "empty".

Say I have argnames <- c("a", "b", "c").

From that I want to construct the equivalent of alist(a=, b=, c=).

Say I have argnames <- c("a", "b", "c").
From that I want to construct the equivalent of alist(a=, b=, c=).

Say I have argnames <- c("a", "b", "c").
From that I want to construct the equivalent of alist(a=, b=, c=).

Here's a one liner that'll do that for you:

argnames <- letters[1:3]
setNames(rep(list(bquote()), length(argnames)), argnames)

- Josh



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Say I have argnames <- c("a", "b", "c").
From that I want to construct the equivalent of alist(a=, b=, c=).

Here's a one liner that'll do that for you:

argnames <- letters[1:3]
setNames(rep(list(bquote()), length(argnames)), argnames)

On Wed, Oct 3, 2012 at 11:21 PM, Josh O'Brien <joshmobrien at gmail.com> wrote:

Say I have argnames <- c("a", "b", "c").
From that I want to construct the equivalent of alist(a=, b=, c=).

Here's a one liner that'll do that for you:

argnames <- letters[1:3]
setNames(rep(list(bquote()), length(argnames)), argnames)

Thanks.

Just so I have my mental model correct, I'm gathering that missing/``
is a symbol that the interpreter has a special rule for -- evaluating
it raises an error, as opposed to objects that evaluate to themselves
or variable names that evaluate to objects.

Does the same sort of thing explain the behavior of `...`? When the
interpreter comes across `...` in the arguments during evaluation of a
call, it trips a special argument-interpolating behavior?

Peter

The R Language definition manual explains all of this. Read it.

Thanks.

Just so I have my mental model correct, I'm gathering that missing/``
is a symbol that the interpreter has a special rule for -- evaluating
it raises an error, as opposed to objects that evaluate to themselves
or variable names that evaluate to objects.

Does the same sort of thing explain the behavior of `...`? When the
interpreter comes across `...` in the arguments during evaluation of a
call, it trips a special argument-interpolating behavior?

Peter

--

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

On Thu, Oct 4, 2012 at 6:12 PM, Bert Gunter <gunter.berton at gene.com> wrote:

The R Language definition manual explains all of this. Read it.

I always reread that before I post to this list.

The only relevant mention of "missing" in the R Language Definition
that I could find were in section 4.1.2 on page 25, and that section

did not answer anything about "missing" as a special symbol (e.g. that
my be put in a formal argument list.)

There is another mention of `...` in section 4.3.2 and it does not

explain some things, such as under what circumstances one would get a
"`...` used in incorrect context" error.

Peter

Thanks.

Just so I have my mental model correct, I'm gathering that missing/``
is a symbol that the interpreter has a special rule for -- evaluating
it raises an error, as opposed to objects that evaluate to themselves
or variable names that evaluate to objects.

Does the same sort of thing explain the behavior of `...`? When the
interpreter comes across `...` in the arguments during evaluation of a
call, it trips a special argument-interpolating behavior?

Peter

--

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

On Thu, Oct 4, 2012 at 6:12 PM, Bert Gunter <gunter.berton at gene.com> wrote:

The R Language definition manual explains all of this. Read it.

I always reread that before I post to this list.

The only relevant mention of "missing" in the R Language Definition
that I could find were in section 4.1.2 on page 25, and that section
did not answer anything about "missing" as a special symbol (e.g. that
my be put in a formal argument list.)

There is another mention of `...` in section 4.3.2 and it does not
explain some things, such as under what circumstances one would get a
"`...` used in incorrect context" error.

Peter

Thanks.

Just so I have my mental model correct, I'm gathering that missing/``
is a symbol that the interpreter has a special rule for -- evaluating
it raises an error, as opposed to objects that evaluate to themselves
or variable names that evaluate to objects.

Does the same sort of thing explain the behavior of `...`? When the
interpreter comes across `...` in the arguments during evaluation of a
call, it trips a special argument-interpolating behavior?

On Thu, Oct 4, 2012 at 6:31 PM, Peter Meilstrup

explain some things, such as under what circumstances one would get a
"`...` used in incorrect context" error.

How could it possibly know that?

-- Bert