Re: Null's not null?
- To: mathgroup at smc.vnet.net
- Subject: [mg69414] Re: [mg69393] Null's not null?
- From: Igor Antonio <igora at wolf-ram.com>
- Date: Mon, 11 Sep 2006 05:39:15 -0400 (EDT)
- Organization: Wolfram Research, Inc.
- References: <200609101120.HAA11248@smc.vnet.net>
- Reply-to: igora at wolf-ram.com
AES wrote:
> Putting Null into one or more slots in a Table and printing the Table
> shows "Null" (without quotes) at the corresponding positions, as also
> does ToString[Null]. I don't think that's what the Help message says:
>
> "Null is a symbol used to indicate the absence of an
> expression or a result. When it appears as an output
> expression, no output is printed."
>
> I can use a string with a couple of empty spaces ("__") to represent an
> occupied but not empty slot in a Table, but that just looks clumsy to
> me. Is there a truly non-printing Null symbol?
The help message is correct. Here's an example:
In[1]:= f[x_] := Null
In[2]:= f[1]
<nothing was returning. no output cell.>
In[3]:= f[5] // InputForm
Out[3]//InputForm=
Null
In the example you mentioned, Null isn't the output of Table. Table
returns a list:
In[6]:= Table[, {i, 0}]
Out[6]= {}
You could use the empty string (""), which won't take up space and won't
be displayed in standardform.
In[7]:= Table["", {i, 5}]
Out[7]= {"", "", "", "", ""}
In[8]:= Table["", {i, 5}] // InputForm
Out[8]//InputForm=
{"", "", "", "", ""}
Igor
PS: Null and "Null" are not the same thing. One case would be when
working with string matching.
--
Igor C. Antonio
Wolfram Research, Inc.
http://www.wolfram.com
To email me personally, remove the dash.
- References:
- Null's not null?
- From: AES <siegman@stanford.edu>
- Null's not null?