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2.6.12 Manipulating Symbols and Contexts by Name
Converting between symbols and their names.
Here is the symbol x.
In[1]:= x // InputForm
Out[1]//InputForm= x
Its name is a string.
In[2]:= SymbolName[x] // InputForm
Out[2]//InputForm= "x"
This gives the symbol x again.
In[3]:= Symbol["x"] // InputForm
Out[3]//InputForm= x
Once you have made an assignment such as x = 2, then whenever x is evaluated, it is replaced by 2. Sometimes, however, you may want to continue to refer to x itself, without immediately getting the value of x.
You can do this by referring to x by name. The name of the symbol x is the string "x", and even though x itself may be replaced by a value, the string "x" will always stay the same.
The names of the symbols x and xp are the strings "x" and "xp".
In[4]:= t = {SymbolName[x], SymbolName[xp]} // InputForm
Out[4]//InputForm= {"x", "xp"}
This assigns a value to x.
In[5]:= x = 2
Out[5]= 
Whenever you enter x it is now replaced by 2.
In[6]:= {x, xp} // InputForm
Out[6]//InputForm= {2, xp}
The name "x" is not affected, however.
In[7]:= t // InputForm
Out[7]//InputForm= InputForm[{"x", "xp"}]
Referring to symbols and contexts by name.
x and xp are symbols that have been created in this Mathematica session; xpp is not.
In[8]:= {NameQ["x"], NameQ["xp"], NameQ["xpp"]}
Out[8]= 
You can specify the form of symbol names using string patterns of the kind discussed in Section 2.7.3. "x*" stands, for example, for all names that start with x.
This gives a list of all symbol names in this Mathematica session that begin with x.
In[9]:= Names["x*"] // InputForm
Out[9]//InputForm= {"x", "xp"}
These names correspond to built-in functions in Mathematica.
In[10]:= Names["Qu*"] // InputForm
Out[10]//InputForm= {"Quartics", "QuasiMonteCarlo", "QuasiNewton", "Quit", "Quotient"}
This asks for names "close" to WeierstrssP.
In[11]:= Names["WeierstrssP", SpellingCorrection->True]
Out[11]= 
Getting rid of symbols by name.
This clears the values of all symbols whose names start with x.
In[12]:= Clear["x*"]
The name "x" is still known, however.
In[13]:= Names["x*"]
Out[13]= 
But the value of x has been cleared.
In[14]:= {x, xp}
Out[14]= 
This removes completely all symbols whose names start with x.
In[15]:= Remove["x*"]
Now not even the name "x" is known.
In[16]:= Names["x*"]
Out[16]= 
Removing all symbols you have introduced.
If you do not set up any additional contexts, then all the symbols that you introduce in a Mathematica session will be placed in the Global` context. You can remove these symbols completely using Remove["Global`*"]. Built-in Mathematica objects are in the System` context, and are thus unaffected by this.
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