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

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9
votes
3answers
676 views

Find subexpression to minimize leafcount after replacment with temporary variable

Given an expression expr, is there an automated way to find a subexpression subexpr such that replacing ...
9
votes
1answer
123 views

Why can't I remove the {0, 0} in Circle[{0, 0}] using pattern matching?

Why does Circle[{0, 0}] /. List[_?NumericQ ..] :> Sequence[] return Circle[{0, 0}] yet ...
9
votes
1answer
358 views

Selectively clear DownValues

How can I clear a subset of a symbol's DownValues ? For example, suppose I have created some DownValues for $f$ like this: ...
9
votes
1answer
248 views

How to define function that can change patterns

Given time series data as follows: data = {{{2011, 1, 13}, 10}, {{2011, 2, 14}, 17}, {{2011, 3, 15}, 20}, {{2012, 1, 16}, 30}, {{2012, 2, 17}, 40}}; ...
9
votes
3answers
123 views

Pattern matching with Complex. Feature or a bug?

fixed in 10.1 (windows) I have run into some strange behavior while doing some pattern matching. First, this works as expected: ...
9
votes
1answer
84 views

Surprising behavior when OptionsPattern is part of a larger pattern

Say we have a pattern defined as: pattern = {foo[OptionsPattern[]] ...}; We can then use MatchQ to see whether an expression ...
9
votes
1answer
261 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 ...
9
votes
0answers
81 views

Strange result of DeleteCases in an association

The function DeleteCases can be used for associations, also with level specification. Here is an example where some values are associations: ...
9
votes
0answers
98 views

Confused by the opts : OptionsPattern[ ] pattern

I'm trying to make sense of the syntax in the clause opts:OptionsPattern[], as found in this standard "rule-based" (pseudo-)function definition pattern: ...
8
votes
2answers
291 views

Unexpected behavior of rule matching a pattern

I am a beginner exploring the world of Mathematica. I expected the following code T[6, 5, 4, 1, 2, 3] /. {T[a___, 1, b___] -> Length[List[b]]} should return ...
8
votes
2answers
222 views

Why does the name of a pattern affect the result of a transformation rule?

I was playing a little dirty, trying to get a template for defining a Curl[] operator. I wrote the following rule, which I knew was going to spit out a few ...
8
votes
3answers
208 views

Select and Blank

I try to filter sublists of a list which match a pattern. test = {{"String1", "a"}, {"String2", "b"}, {"String3", "a"}, {"String4", "a"}}; The result should ...
8
votes
4answers
288 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 ...
8
votes
3answers
505 views

How can I convert x^2 to x*x?

When I try the following code: a b^2 c /. b c -> e Mathematica gives me: a b^2 c but what I want is: ...
8
votes
2answers
268 views

Matching pair of numbers {a,-a}, where a is numeric

Imagine you have a list of pairs of numbers, such as {{2,-2}, {1,5}, {1,-3},{-3,3}} The task is to reduce the given list to a list of pairs of type ...
8
votes
1answer
159 views

CSS Selectors for Symbolic XML

Symbolic XML is a convenient way of managing XML in Mathematica, at least for casual use or small tasks. Here and elsewhere you can find examples of XML handling in Mathematica, including XSLT/XPath ...
8
votes
2answers
246 views

Replacing product expressions - named vs. unnamed pattern?

Suppose I have an expression of the form a b c d + x y z The FullForm of this is ...
8
votes
1answer
238 views

Is it possible to specify a context-sensitive, “depth-agnostic” rewrite rule?

I'm using the term "depth-agnostic" in this post to describe structural patterns featuring a "target" sub-pattern that can occur "at any depth" relative to one or more "context" sub-patterns. As a ...
8
votes
1answer
285 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
208 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
2answers
761 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 ...
8
votes
1answer
127 views

How to get a list of all expressions in a notebook matching a certain pattern?

Suppose I have a Mathematica notebook saved to a certain location on disk. Given a pattern I need to get the list of all expressions matching this pattern that appear in input, output or print cells ...
8
votes
2answers
421 views

Adapting “Find and Replace” functionality to work with Patterns

I was thinking if there is something like Find and Replace (Crtl+F) functionality adapted to work with patterns. Probably not, but it seems possible to create this with some effort and skills in ...
8
votes
1answer
231 views

Transformation rule on a list of non-negative integers

I am trying to create a transformation rule that takes a list of non-negative integer values of any length, finds a non-zero entry in the list, adds 1 to all preceding numbers, subtracts 1 from the ...
8
votes
1answer
321 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: ...
8
votes
1answer
267 views

How does Mathematica wrap code for front-end needs? Why does this wrapping affect the evaluation?

Mathematica wraps any expression with some boxing code before showing the evaluation result in the front-end. Unfortunately, the wrapping algorithm and its position in the Mathematica end-to-end flow ...
8
votes
2answers
139 views

An equivalent to Condition that I can use anonymously when string pattern matching

When I name a pattern I'm working with, that name stands for the same particular expression wherever it shows up. That's a basic precept of how the Wolfram Language's pattern-matching works. But if I ...
8
votes
2answers
411 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 ...
8
votes
1answer
300 views

Mma10 mystery: Failure of pure function substitution with Interpretation?

Bug introduced in 10.0.0 and fixed in 10.0.1 I had code to display with subscripts from Displaying index as subscript on output: e.g. C[i] -> C_i with Notation[...] or Interpretation[..]? which ...
7
votes
5answers
544 views

Calculating weird numbers

A weird number is a number such that the sum of the proper divisors (divisors including 1 but not itself) of the number is greater than the number, but no subset of these divisors sums to to ...
7
votes
5answers
424 views

Find patterns in a list

again, I have a list like this: ...
7
votes
5answers
422 views

Splitting strings at lower case characters and numbers

I'm trying to split the strings of chemicals into their elements and numbers. See this example "Fe3O4" will be split into ...
7
votes
3answers
238 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 ...
7
votes
4answers
445 views

Strange answer from StringReplace

I have a list of strings and I would check if there is an empty string element, that's "", because I need to replace it with a "0". I try the following ...
7
votes
2answers
272 views

Using MatchQ (or other means) to parse an expression using sums of COS or SIN correctly

I am writing a function that will take an expression as input. I want to make sure the expression is valid first before processing it. Looking for a correct to use ...
7
votes
4answers
751 views

How to collect terms with positive powers in polynomial

I am trying to collect all terms with non-negative powers of $x$ in polynomials like $\frac{1}{x^2}\left(a x^2+x^{\pi }+x+z\right)^2$ First expand the polynomial ...
7
votes
3answers
237 views

Why these ways of defining a function with variable number of arguments fail?

First: I know about the correct way to define a function with variable number of arguments: Clear[f] f[s__] := Plus[s] f[1, 2, 3, 4] (* 10 *) BUT I ...
7
votes
3answers
146 views

Pattern matching: Times[a_] vs Times[a__]

I don't understand why MatchQ[ HoldComplete[Times[3, 2, 2]], HoldComplete[Times[a_]] ] is returning True. I thought that ...
7
votes
2answers
224 views

How can I construct a recursive pattern guard?

I am modelling binary trees in Wolfram Language by writing them as three-element lists, like so: binTree = {nodeVal, leftChild, rightChild}. It does not yet matter ...
7
votes
3answers
164 views

Checking through an expression

I am writing a code that manipulates expressions that contains functions with an arbitrary number of arguments. An example expression is ...
7
votes
1answer
147 views

LetterCharacter for Cyrillic symbols

Why does the code StringMatchQ["ы", LetterCharacter] return False? Probably because: ...
7
votes
1answer
229 views

Built in way to de-list singletons?

Is there a built in method to de-list singleton expressions, like this rule-based solution: expr_ :> If[Length[expr] == 1, First@expr, expr] In data ...
7
votes
1answer
822 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. ...
7
votes
1answer
120 views

How to debug this failing pattern-matching expression?

NB: this question is primarily about troubleshooting and debugging, and only secondarily about pattern-matching. IOW, I'm far less interested in getting an explanation for the situation described ...
6
votes
5answers
434 views

The correct pattern for Cases

I have a problem that, admittedly, I have already solved using Select instead, but it is irking me that I cannot seem to construct the right pattern to solve it ...
6
votes
6answers
519 views

Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
6
votes
3answers
339 views

String matching balanced pairs of braces

I am trying to extract from a string in Mathematica all instances of \newcommand{ABC}{DEF} Where ABC and ...
6
votes
4answers
307 views

Is there a more Mathematica-y way to label these plots?

I am studying an infinite square well in the context of quantum mechanics. ...
6
votes
2answers
229 views

Is it possible to use PatternTest and Optional value on one Pattern simultaneously? [duplicate]

Possible Duplicate: How to Combine Pattern Constraints and Default Values for Function Arguments First a simple example: define a function "add" with two arguments, and its second argument ...
6
votes
4answers
324 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 ...