Re: Null's not null?
- To: mathgroup at smc.vnet.net
- Subject: [mg69415] Re: [mg69393] Null's not null?
- From: Igor Antonio <igora at wolf-ram.com>
- Date: Mon, 11 Sep 2006 05:39:18 -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?