2.7.12 Manipulating Symbols and Contexts by Name
| Symbol["name"] | construct a symbol with a given name | | SymbolName[symb] | find the name of a symbol |
Converting between symbols and their names. | Here is the symbol x. | |
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| Its name is a string. | |
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SymbolName[x] // InputForm
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| This gives the symbol x again. | |
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Symbol["x"] // InputForm
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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
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| This assigns a value to x. | |
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| Whenever you enter x it is now replaced by 2. | |
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{x, xp} // InputForm
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| The name "x" is not affected, however. | |
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| NameQ["form"] | test whether any symbol has a name which matches form | | Names["form"] | give a list of all symbol names which match form | | Contexts["form`"] | give a list of all context names which match form |
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"]}
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You can specify the form of symbol names using string patterns of the kind discussed in Section 2.8.4. "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
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| These names correspond to built-in functions in Mathematica. | |
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Names["Qu*"] // InputForm
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| This asks for names "close" to WeierstrssP. | |
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Names["WeierstrssP", SpellingCorrection->True]
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| Clear["form"] | clear the values of all symbols whose names match form | | Clear["context`*"] | clear the values of all symbols in the specified context | | Remove["form"] | remove completely all symbols whose names match form | | Remove["context`*"] | remove completely all symbols in the specified context |
Getting rid of symbols by name. | This clears the values of all symbols whose names start with x. | | |
| The name "x" is still known, however. | |
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| But the value of x has been cleared. | |
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| This removes completely all symbols whose names start with x. | | |
| Now not even the name "x" is known. | |
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| Remove["Global`*"] | remove completely all symbols in the Global` context |
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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