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

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14
votes
3answers
236 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
496 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
104 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: ...
16
votes
1answer
440 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 ...
0
votes
1answer
405 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 ...
15
votes
2answers
407 views

Successful match in Replace but not in Cases?

I have a little example that exhibits a successful pattern match in ReplaceAll that Cases misses and I wonder if the assembled ...
8
votes
2answers
360 views

How to Enable Syntax Coloring of Pattern Match Variable Only (i.e. Without Coloring any Associated Pattern)?

Syntax coloring for the following function definition foo[x_List] := ... will color green (and italicize by default) the argument name ...
15
votes
1answer
653 views

How to Combine Pattern Constraints and Default Values for Function Arguments

EDIT: As several respondents have noted in the answers and comments below, the original example had a default value that would never be used because of the way patterns and default values are ...
16
votes
1answer
313 views

Is pure pattern matching without PatternTest and Condition Turing-complete?

Note that this question is not a duplicate of that one. It is specifically about the pattern-matching engine, and explicitly excluding those patterns which call back into the full evaluation (i.e. ...
8
votes
1answer
261 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
199 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
302 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
291 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
242 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 ...
6
votes
4answers
262 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 ...
9
votes
2answers
220 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
226 views
12
votes
2answers
322 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 ...
-2
votes
1answer
203 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
288 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 ...
4
votes
1answer
298 views

Path queries for tree-structured data

Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data? Suppose data is organized hierarchically in key->value pairs, eg: ...
4
votes
1answer
102 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. ...
15
votes
6answers
865 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 ...
17
votes
6answers
682 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 ...
40
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 ...
13
votes
2answers
640 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_] := . . ...
15
votes
4answers
713 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 ...
17
votes
2answers
533 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
177 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
221 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. ...
8
votes
2answers
651 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 ...
7
votes
1answer
666 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. ...
34
votes
9answers
1k views

Injecting a sequence of expressions into a held expression

Consider the following toy example: Hold[{1, 2, x}] /. x -> Sequence[3, 4] It will give Hold[{1, 2, Sequence[3, 4]}] ...
10
votes
3answers
748 views

Passing down arguments

In R, one can use ... to pass arguments down to another function. For example ...
41
votes
4answers
2k views

Using a PatternTest versus a Condition for pattern matching

My last question to the site resulted in several answers that involve using pattern matching in Mathematica, a feature I wasn't very familiar with at the time. I am currently reading Mathematica ...
19
votes
1answer
409 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
311 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 ...
8
votes
4answers
266 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 ...
19
votes
2answers
1k 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
426 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 (...
46
votes
4answers
1k views