Wolfram Function Repository

Instant-use add-on functions for the Wolfram Language

Function Repository Resource:

 AssociationReference

Source Notebook

Create an association with self references

Contributed by: Bob Sandheinrich

ResourceFunction["AssociationReference"][key]

represents a reference to another value in an Association.

ResourceFunction["AssociationReference"][<|k1⧴val1,k2⧴val2,…|>]

represents an Association where instances of ResourceFunction["AssociationReference"][ki] within the valj are resolved to the values vali.

Details

ResourceFunction["AssociationReference"] can reduce the size of an Association by eliminating repeated large values.
Any vali expressions containing ResourceFunction["AssociationReference"] should be defined using RuleDelayed.

Examples

Basic Examples (2) 

Create an AssociationReference object with three keys, two of which reference the other:

In[1]:=
as = ResourceFunction[ "AssociationReference"][<|"numbers" -> Range[100], "max" :> Max[ResourceFunction["AssociationReference"]["numbers"]], "min" :> Min[ResourceFunction["AssociationReference"]["numbers"]]|>]
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In[2]:=
as["max"]
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In[3]:=
as["min"]
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In[4]:=
as["numbers"]
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In[5]:=
as = ResourceFunction[ "AssociationReference"][<|"numbers" -> Range[100], "max" :> Max[ResourceFunction["AssociationReference"]["numbers"]], "min" :> Min[ResourceFunction["AssociationReference"]["numbers"]], "range" :> (ResourceFunction["AssociationReference"]["max"] - ResourceFunction["AssociationReference"]["min"])|>]
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In[6]:=
as["range"]
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In[7]:=
as["min"]
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In[8]:=
as["numbers"]
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Scope (4) 

Many functions work on AssociationReference objects like on Association objects:

In[9]:=
as = ResourceFunction[ "AssociationReference"][<|"numbers" -> Range[100], "max" :> Max[ResourceFunction["AssociationReference"]["numbers"]], "min" :> Min[ResourceFunction["AssociationReference"]["numbers"]]|>]
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Part gives values:

In[10]:=
as[["min"]]
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Key limiting operations return a new AssociationReference object:

In[11]:=
KeyTake[as, {"max", "numbers"}]
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In[12]:=
KeyDrop[as, {"max"}]
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In[13]:=
Keys[as]
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In[14]:=
Select[as, ListQ]
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In[15]:=
Select[as, OddQ]
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In[16]:=
DeleteDuplicatesBy[ ResourceFunction[ "AssociationReference"][<|"a" -> 1, "b" -> -1, "c" :> ResourceFunction["AssociationReference"]["a"], "d" -> -2|>], Abs]
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Values and Normal return the final value for each key:

In[17]:=
Values[as]
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In[18]:=
Normal[as]
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In[19]:=
KeyExistsQ[as, "max"]
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A few basic statistical operations are supported:

In[20]:=
as = ResourceFunction[ "AssociationReference"][<|"a" -> 10, "b" :> 2* ResourceFunction["AssociationReference"]["a"], "c" :> ResourceFunction["AssociationReference"]["b"]/4|>]
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In[21]:=
Through[{Mean, Max, Min, Total, Variance, MinMax, Median}[as]]
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In[22]:=
Quantile[as, 3/4]
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Sorting operations return a new AssociationReference object:

In[23]:=
Sort[ResourceFunction[ "AssociationReference"][<|"a" -> 3, "b" -> 2, "c" -> 1|>]]
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In[24]:=
KeySort[%]
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In[25]:=
Prepend[ResourceFunction[ "AssociationReference"][{"cow" -> "moo", "chicken" -> "cluck"}], "horse" -> "neigh"]
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Use Map to map a function over values:

In[26]:=
as = f /@ ResourceFunction[ "AssociationReference"][<| "Capitol" -> Entity["City", {"JeffersonCity", "Missouri", "UnitedStates"}], "LargestCity" -> Entity["City", {"SaintLouis", "Missouri", "UnitedStates"}], "Ratio" :> ResourceFunction["AssociationReference"]["LargestCity"]/ ResourceFunction["AssociationReference"]["Capitol"]|>]
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In[27]:=
as // InputForm
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When the value is retrieved, the function is applied on each value:

In[28]:=
as["Ratio"]
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Possible Issues (2) 

If keys are removed, the resulting AssociationReference object can give values with Missing instead of the dependency:

In[29]:=
as = KeyTake[ ResourceFunction[ "AssociationReference"][<|"three" -> 3, "two" :> ResourceFunction["AssociationReference"]["three"] - 1|>], "two"]
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In[30]:=
as["two"]
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Loops are bad:

In[31]:=
ResourceFunction[ "AssociationReference"][<| "key" :> ResourceFunction["AssociationReference"]["key"]|>]["key"]
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Version History

  • 1.0.0 – 08 July 2022

Related Resources

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