Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.

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39
votes
1answer
1k views

How to generally match, unify and merge patterns?

This question was split from this one. While that question is now about how to match two particular patterns (mostly using Verbatim or ...
3
votes
1answer
155 views

Pattern matching a multivariate derivative

I can extract the parameters of a single variable derivative with the rule D[f[x], x] /. Derivative[order_][fcn_][variable_] -> {order, fcn, variable} ...
9
votes
1answer
240 views

Mixing patterns with string patterns

I have imported an XML document into Mathematica. It is now represented as Symbolic XML expression in the variable xml: ...
5
votes
2answers
193 views

Pattern matching deletion of list items [duplicate]

Possible Duplicate: How can I remove B -> A from a list if A -> B is in the list? I'm working toward building a graph and use some code to construct my rules which results in a form ...
11
votes
2answers
251 views
2
votes
2answers
267 views

Pattern test for variables during function definition

I am having a problem with pattern testing on variables during function definition ...
10
votes
4answers
380 views

Calling Table with custom iterator

I often find myself in situations where I, for example, need to build a table for some expression, but want to set the number of points rather then the step size, so the code ends up looking like this ...
16
votes
4answers
408 views

Splitting a list

Please consider the following list: data={1, 0, 0, 0, 2, 5, 2, 3, 0, 0, 3}; Now I would like to split the list into 0-sequences and Not-0-sequences as following: ...
5
votes
5answers
344 views

How can I use nested conditionals inside my functions?

I'm a big fan of using conditionals inside my functions to deal with cases, that is, to pattern match in stages and possibly leave a function unevaluated. ...
16
votes
1answer
408 views

NotebookFind and String Pattern Expressions

Is there a way that NotebookFind can be used to match string pattern expressions rather than just strings? The documentation for ...
4
votes
1answer
146 views

Searching Notebooks for String Patterns using Workbench v2

The Workbench webpage describing new features in version 2 lists the ability to "Search notebook documents with the Mathematica pattern search utility" under the heading Mathematica Front End ...
7
votes
3answers
207 views

Pattern matching Q for rectangular data matrices

Given a List of rectangular nx3 arrays of data, each of the form {...,{x,y,z},...}, (the ellipses are not Mathematica pattern syntax, just for illustration). Some members of this list may be - by ...
3
votes
1answer
134 views

Set promotes Rule to RuleDelayed?

In mentally building a model of how Mathematica works, I naively expected Set to create a Rule in a symbol's ...
12
votes
2answers
302 views

Split a Unicode string maintaining uppercase characters

I want to split a string according to a predefined set of substrings (lowercase), though the actual text can contain uppercase characters anyplace. The task is to find the matches, longer preferred ...
14
votes
2answers
439 views

Pattern issues weird warning

Take for example head[b_[PatternSequence[_, _]]] := 9 I know this example serves no purpose as is. It also happens in useful examples such as ...
8
votes
1answer
224 views

Creating a version of SequenceAlignment that accepts patterns

SequenceAlignment seems like a function that is not (yet?) fully integrated into Mathematica. I want a function that accepts general patterns instead. I ...
14
votes
3answers
233 views

What's wrong with this pattern of the form Except[Repeated[…]]?

I'm trying to build a head that recognizes molecules. Here's the code ...
11
votes
3answers
451 views

Delete duplicates in a list, depending on the sequence of numbers

Below, list is a representative sample of my list, which contains lists of integers. I would like to be able to input: ...
2
votes
2answers
95 views

Using FreeQ with implicit functions

In Mathematica 7, I want to determine whether a list of free of numbers greater than 1 or not. It seems like using FreeQ would be a concise way to do this: ...
0
votes
1answer
360 views

What does the slash-colon symbol do?

I came across a bit of code that uses the syntax /: and I don't know what it does. I can't find its documentation, or maybe I'm just not looking properly. The code ...
16
votes
6answers
652 views

Split a string at specific positions

Given a string of alphanumerical characters, how to split it simply and quickly at the center of continuous letter-substrings? Is there an elegant and fast solutions out there in the "computational ...
8
votes
1answer
250 views

Does Mathematica use first order or second order order unification?

When Mathematica is pattern-matching expressions, does it use first order or second order unification. Just to clarify the difference between first order and second order unification: In Second order ...
8
votes
1answer
188 views

MatchQ and patterns for similar lists

I can't seem to find the right set of patterns to independently match two different lists. Simplified versions of the lists are as follows: ...
8
votes
1answer
300 views

Why does Mathematica choose the second function definition?

While working on a solution to this question I've come across a case where I simply don't understand Mathematica's behaviour. I've got the following definitions: ...
10
votes
6answers
280 views

How can I mix the behaviors of StringReplace and ReplaceAll in a single rule?

I'm trying to take a list of the form { {"65 + 3 months", 75}, {"65 + 4 months", 75.1} }, and transform the string part to a number such as 65.25 or 65.333, ...
9
votes
3answers
227 views

Splitting a list in which figures vary from negative to positive

Consider the following list: data={4078, 256, -1266, -388, 1290, 1368, 1446, 1524, 2}; I would like to split any kind of such list always, when figures turn form ...
9
votes
2answers
203 views

Why doesn't Cases match all instances of XMLElement, given Infinity levelspec?

Why doesn't Cases match all instances of XMLElement, given Infinity levelspec? ...
4
votes
1answer
98 views

How do you set an Optional parameter with a global variable on a Function defined in a Package

In a Package I am writing, I'm trying to define a function with an Optional parameter in it that is set to a global variable. ...
6
votes
4answers
238 views

How to match a sequence of complex patterns?

I have list with the form {{a1,b1}->{x1,y1},{a2,b2}->{x1,y2},...} where the {ai,bi}'s can be ...
8
votes
4answers
252 views

Check in a series if there exists adjacent values with less than a certain number of missing values

I'm working with a large number of series of different experiments, where there exist a lot of experiments where there are no entries. I now want to draw a sample where there should exist at least ...
-2
votes
1answer
194 views

How to set a rule in pattern matching to change a string from one form to another

I want to define a rule that will change a particular type of string to another form. For example:- a string having ...
4
votes
2answers
283 views

Why can't NumberQ be used as the head of a pattern?

Consider the following: list={1/First[{}], 1, 2, 1/First[{}], 3}; DeleteCases[list,_NumberQ] I wanted to remove all cases, which did not match ...
22
votes
5answers
1k views

Fetching data from HTML source

I want to generate a couple of plots/graphs with Area51 statistics. Since Area51 doesn't work with the SE API, I'm forced to find another way to get the information I want. That other way is with ...
14
votes
6answers
768 views

Using patterns in pure functions

Pure functions may be handy if you don't want to assign your function a name. For example I would calculate $x(x-1)$ for some numbers $x$ by ...
14
votes
4answers
669 views

How to match a pattern with a pattern?

UPDATED This question is about: "What is the pattern to match a pattern-definition, exactly as it is written?" My original question is now split according to Mr.Wizards insightful answer below. This ...
13
votes
2answers
556 views

How to use subscript in pattern names?

For example I want to define a function with parameters σx and σy, that is, the function will be declared as: f[σx_,σy_] := . . ...
8
votes
2answers
610 views

Mathematica rule substitution memory

First I present the specific programming question, and then I provide further background details. Given an expression in Mathematica, say f=3x+7y, there are two ...
17
votes
2answers
492 views

How to inject an evaluated expression into a held expression? [duplicate]

I know that there are methods to structurally manipulate held expressions (discussed e.g. here), but I failed to apply those for this particular problem: ...
0
votes
1answer
173 views

How to use Function[] in MatchQ[] and control argument's evaluation? [duplicate]

Possible Duplicate: Why doesn't PatternTest work with Composition? ...
6
votes
1answer
214 views

How to set up new types for pattern matching strings?

Consider the following toy example: I have a set of language sounds, which I partition into two exclusive subsets, consonants and vowels. I want to set up string patterns for e.g. ...
7
votes
1answer
623 views

Extracting coefficients from a partial differential equation

Frequently, I come across the following problem: How to rewrite a complicated partial differential equation in a more clear way? I would like to create some order by collecting terms that are equal. ...
19
votes
1answer
381 views

Why doesn't PatternTest work with Composition?

While playing around with the solutions to this question, I've found some very strange behaviour: ...
6
votes
3answers
288 views

Replacement rule only matches part of expression

I have the result of a calculation (which is too long to mention here) and it gives ...
19
votes
2answers
974 views

Pattern to match a non-empty list of non-empty lists

Is there a pattern to match a list of lists, containing at least one list, with each list containing at least one element? In the Mathematica documentation it says that the pattern ...
23
votes
2answers
413 views

How can I ensure that I am constructing patterns in the most efficient way possible?

Inspired by this answer, I am interested to know if there are best practices or rules of thumb for constructing patterns, for example for use in function definitions (...