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

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3
votes
3answers
289 views

How to identify all rules that match pattern type? [duplicate]

I would like to be extend the below solution to be able to find get all rules from the list step[2] that match the generic pattern k_Digit_p. Where k and p are not ...
1
vote
1answer
60 views

How to use EvenQ[] in patterns? [duplicate]

This works: (w[1] + w[2] + w[3]) /. w[s_] -> If[s == 2, w[s], 0] (* w[2] *) This doesn't: ...
7
votes
1answer
146 views

How to Negate a Pattern Test and Transform a List of Strings to a JSON array

First I would like to find out how to negate a pattern and based on this I would like to solve this little problem on how to transform a list of strings to a JSON array. This is how I started working ...
0
votes
2answers
105 views

Delete Element within a List based on the Order [closed]

I want to do the following, deleting the element of a list that do not match an increasing order as example: {1,2,3,4,6,5,7,8}->{1,2,3,4,6,7,8} I've thought of using DeleteCases but I'm not able to ...
5
votes
2answers
404 views

Opposite of Alternatives

I was looking at this question (here) and I tried to find any thing gives the opposite of Alternatives. In other words, some pattern matching function that gives ...
22
votes
4answers
336 views

Is there a GraphicsPrimitiveQ (or a complete list of Heads of graphics primitives)?

For various reasons related to workflow associated with creating figures for journals, I am creating functions that will accept graphics primitives and a set of options and spit out a ...
2
votes
2answers
195 views

How to make a function that yields a number under power operator by using pattern matching?

Can I ask you a question related to function and pattern? I would like to make the function below work which doesn't yield return values I expect. How can it be done? ...
4
votes
2answers
185 views

Is there any way to use head of Real and Integer altogether?

Is there any way to use the head of Integer and Real together like below? The below is not right, I know that, it is just for ...
2
votes
1answer
147 views

Why is there a difference when formulating patterns for Select and FirstPosition?

Select[{1, 2, 4, 7, 6, 2}, # > 2 &] Gives {4, 7, 6}. OK! So one should think that the following would work: ...
3
votes
1answer
56 views

Remove cases where region specified incorrrectly

I am using MeshPrimitives to get a list of 3D components of a Mesh Region. Within that list, I normally get some incorrectly specified regions, such as ...
7
votes
1answer
140 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 ...
9
votes
0answers
96 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: ...
0
votes
0answers
16 views

Comparing association using MatchQ [duplicate]

For me below query results into False.I expect it to return True. ...
3
votes
2answers
121 views
8
votes
3answers
404 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
1answer
128 views

Is there an elegant way of delaying evaluation of `A==B` when calling a function that uses this pattern

Suppose I wanted to define a number of functions that accepts expressions of the form: ...
1
vote
2answers
77 views

What is the role of the pattern object in this implementation?

In the documentation I found a nice idiom which allows me to do model fitting with interpolating functions. I think this kind of thing is amazing and a credit to the utility of an environment like ...
3
votes
3answers
77 views

How to exclusively match in the numerator?

Here is an expression (one of many) that involves two complicated terms: \begin{multline}\text{expression} = \frac{\log \left(\frac{c}{d}\right) \left(2 a d F(a,b,c)+a^2 \left(a^2-2 a (b+c)+b^2+4 b ...
18
votes
4answers
899 views

How to define a recursive pattern?

I want to translate this recursive syntactic definition into a Mathematica pattern1: $$ \mathtt{x}: \begin{cases} \text{Null}\\ \{\textit{integer}, \mathtt{x}\} \end{cases} $$ In other ...
1
vote
0answers
58 views

Why has FreeQ a quadratic complexity with high depth?

I am a little puzzled by the following test: ...
2
votes
2answers
191 views

Two ways to speed up slow Integrate[]s? (Can't do either)

I run into problems like this all the time on the complicated integrands I pass to Integrate. The following code works but takes a veeery looong time: ...
9
votes
0answers
150 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: ...
1
vote
0answers
41 views

What does __Rule do in Mathematica? [closed]

What does __Rule do in mathematica? I understand the __ is used for any repeated expression, but why is the Rule appended at the end? For example: Import nested JSON file Thanks!
0
votes
2answers
117 views

Match groups in regular expressions

I'm trying to understand Mathematica's pattern matching in strings, but I have some doubts. 99% of the time I need to a) check if a match occurs and b) retrieve the matched patterns. I come from ...
1
vote
0answers
116 views

How to Pattern Match complicated patterns? [closed]

How can I get the output expressed in terms of p1 and p2 instead of exponentials? ...
3
votes
1answer
114 views

How to write a pattern that matches all functions

What is the correct way to match a function in an expression in the way that Cases[Sin[x] Cos[x], _Sin | _Cos, {0, Infinity}] matches ...
5
votes
1answer
73 views

Ordering in noncommutative multiply

I have an expression like s ** p1 ** p1 ** p2 - s ** p1 ** p2 ** p1 Which should be zero because the commutator between p1 ...
3
votes
3answers
114 views

How to apply ReplaceAll to denominator?

Here is the simple task. In reality, it's far more complicated, but it comes down to this. I want to take the expression $\frac{y}{x^2}$ and replace $x^2$ with $k$. This doesn't work: ...
2
votes
1answer
102 views

Pattern matching list of elements with different heads

I have a function, which I want to accept only a list of kind of elements belonging to a group. The task comes down to finding an elegant pattern suitable for easy to read function prototype. As an ...
1
vote
1answer
60 views

Emulating Case Pattern replacement

As most regular users, I have developed utility functions complementing the Wolfram language for frequent tasks. In particular, I have variations on Cases (see ...
4
votes
1answer
202 views

Sow only if different from zero

I am trying to collect elements with Reap and Sow, where I am interested only in non-zero elements, that is I am trying something like that ...
4
votes
1answer
87 views
0
votes
0answers
41 views

Where can I find mathematica documentation about @@@? [duplicate]

For example, to build a rule from 2 lists {a,b,c},{1,2,3},I use : Rule @@@ Transpose[{{a, b, c}, {1, 2, 3}}] : {a -> 1, b -> 2, c -> 3} OK, but how @@@ works ? (Black magic for me) I am using ...
2
votes
1answer
54 views

Pattern matching & simple replacement

I have a question about an expression that I want to modify. Here is the expression: ...
4
votes
1answer
76 views

Using patterns to modify TeXForm output

When I use TeXForm on a matrix I often want to replace some the output with some number of verticle and horizontal lines. Is there a way to get control over this, possibly using patterns? As an ...
2
votes
2answers
81 views

Evaluation speed of apparently equivalent functions

Consider the following expressions: f[x_Integer] := x, f[x_] := x /; x ∈ Integers, f[x_?IntegerQ] := x All of the expressions above (and probably others which ...
0
votes
1answer
68 views

Generate all 3-permutations of the set {x, y, z, w, u, t} excluding the ones where 'u' is after 't' [closed]

I have to generate all 3-permutations of a the set $(x, y, z, w, u, t)$ without the ones where the element $u$ is after element $t$. So far I have generated all the the 3-permutations like such <...
0
votes
1answer
100 views

Applying ReplaceAll to I (imaginary unit) [closed]

Why does I/.I->-I return -I but Exp[-I]/.I->-I yields ...
1
vote
2answers
107 views

Get the sum with cases

I have the following list: list = {{1, 2}, {2}, {3, 4, 1}, {5, 4}, {3, 3}, {a, b, c}, {e, f}, {g}, {}, {Sin[a], Cos[b]}}; I should use ...
-3
votes
2answers
109 views

Write a function, write a pattern [closed]

I have the following list: list = {{1, 2, 4}, 6, 7, 8, {8, 2}, {3, 4}, {4, 5}, {1, 2, 3, 1}}; (a) I should write a predicate-function in combination with an ...
0
votes
1answer
51 views

Find/Write a pattern [closed]

I should find a pattern for the following expression: expr = {a^2, a^b, x^4, (x - 1)^2}; And that should be the result: ...
9
votes
1answer
96 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 ...
1
vote
2answers
94 views

Removing solutions which are particular cases of others

I have an algorithm which gives me a list of solutions (in matrix form, if it is of any importance) of an equation. Some of these solutions are particular cases of other. For example, in this list ...
1
vote
1answer
121 views

Dealing Repeated pattern in StringReplace

A problem about StringReplace When I'm running into this problem possible [bug] ...
0
votes
4answers
177 views

How to trim the zeros from the right of a list? [duplicate]

I need to remove the zeros from the right of an integer list up to the first non-zero element. Such as {0,1,0,0,2,0,0}->{0,1,0,0,2}. Padding zeros can be simply ...
4
votes
0answers
118 views

Why the flat f[x] is treated as ghostHead_[f[x]]?

While reading this answer I feel confused. If we do not care any specific detail of the original question, then ybeltukov's answer essentially makes use of the following fact ...
15
votes
6answers
1k views

Finding the period of an array of integers

A simple array of integers is given. The problem is to detect if a pattern is repeatedly occurring in the array, and find the length of that pattern. For example, for ...
0
votes
1answer
92 views

Can we say that “all functions in Mathematica are some kind of pattern-matching-and-replacement procedures”? [duplicate]

Currently I am studying Mathematica programming, and when I study pattern matching and replacement, I find it is quite similar to functions. So can we say "all functions in Mathematica are some kind ...
11
votes
1answer
307 views

Empty Blank regression in v10.1

Bug introduced in 10.1 and fixed in 10.2.0 In v10.1.0.0 on Linux, when Blank[] is used in Alternatives with pattern that can ...
4
votes
4answers
159 views

Express block matrix in terms of matrix basis

I'm trying to construct a function that returns the multiplication table of a matrix Lie algebra. Assuming a basis of matrices, my definitions: ...