Shortest

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`Shortest`

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Shortest[p]

is a pattern object that matches the shortest sequence consistent with the pattern p.

Details

Shortest works for both ordinary expression patterns and string patterns.
If several Shortest objects occur in the same expression, those that appear first are given higher priority to match shortest sequences.
Shortest[p,pri] is given priority pri to be the shortest sequence. Matches for shortest sequences are tried first for Shortest objects with higher priorities.
Priorities can be any expression, and are ordered in standard Wolfram Language Sort order. Shortest[p] specifies the highest possible priority.
Shortest objects with equal priorities are tried in the order they appear in the expression.
If no explicit Shortest or Longest is given, ordinary expression patterns are normally effectively assumed to be Shortest[p], while string patterns are assumed to be Longest[p]. »
Shortest has special meaning when combined with Optional. Shortest[patt:def] first attempts to match using the value def and only then tries the pattern patt. If Optional is used with no explicit Longest or Shortest, it is effectively wrapped in Longest. »
For ordinary expressions, Shortest[p] specifies that not just p itself, but also all parts of p should match the shortest sequences.
Shortest[p] corresponds to a "non-greedy pattern".
Shortest[p] may not correspond to the absolutely shortest expression matching p if there are additional constraints elsewhere in the pattern.

Examples

open allclose all

Basic Examples (1)Summary of the most common use cases

Control ambiguous matches by using Shortest:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-b2lty

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-icic1b

Out[2]=2

Scope (2)Survey of the scope of standard use cases

Shortest works with string patterns:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-jgvkq4

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-kh0al7

Out[2]=2

Use priorities to affect ambiguous choices:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-br5bds

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-t0nee

Out[2]=2

Applications (1)Sample problems that can be solved with this function

Consider the following variable-length argument function:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-mhkrm0

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-dwqh5g

In[3]:=3

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https://wolfram.com/xid/0wf8p8s-n38q1

Out[3]=3

Use Shortest to express it as one pattern:

In[4]:=4

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https://wolfram.com/xid/0wf8p8s-ch0wme

In[5]:=5

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https://wolfram.com/xid/0wf8p8s-s4uuh

Out[5]=5

Properties & Relations (4)Properties of the function, and connections to other functions

For expressions, when a pattern has consecutive sequences, the first one is effectively wrapped in Shortest:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-r3uqlm

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-x2p221

Out[2]=2

For string patterns, Shortest provides "non-greedy" or "lazy" matches of all minimum-length matches:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-qy1ll4

Out[1]=1

For ordinary patterns, most patterns are effectively wrapped in Shortest:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-t3nmk2

Out[1]=1

String patterns are effectively wrapped in Longest:

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-kiw4he

Out[2]=2

By default, patt:def first attempts the pattern using patt and only then def:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-gxdfrp

Out[1]=1

When Shortest is combined with Optional, the order is reversed:

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-6cl2sw

Out[2]=2

Possible Issues (3)Common pitfalls and unexpected behavior

When there are additional constraints, Shortest may not match the absolute shortest sequence:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-hfeevi

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0wf8p8s-xt0vcn

Out[2]=2

For string patterns, Shortest will match all minimal substrings, not just the absolute shortest match:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-il1ikv

Out[1]=1

Priorities are not supported in string expressions:

In[1]:=1

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https://wolfram.com/xid/0wf8p8s-sesren

Out[1]=1

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