Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,030
questions
0
votes
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37 views
Identifying repeating patterns in a list of numbers
I have some generated lists of natural numbers which have a small number of distinct values, ie. referencing the variable "rowToCheck" for each list:
list1: rowToCheck = 3: length=7, distinctvalues=3
...
0
votes
0answers
29 views
Delayed Rule right-hand-side mis-evaluation
Outline
I am trying to create a rule that will give me a minus sign if the number of times A is applied on X is odd where A is some οperator and X a random quantity.
Some of the configurations of ...
3
votes
1answer
26 views
Condition in SparseArray does not check the condition for some matrix elements
Consider the following MWE:
SparseArray[{{i_, j_} /; (IntegerDigits[i - 1, 2, 2][[1]] == 0) :> 1}, {4, 4}]
This should give a $4\times 4$ matrix in which the ...
2
votes
1answer
65 views
Pattern Matching, FullForm and DisplayForm
Has anybody an explanation for the following or is it a bug?
The display form and the input form do not give the same result.
I include the raw display form here. Simply copy it to Mathematica to ...
6
votes
1answer
83 views
ReplaceList Except Alternatives bug
Bug introduced in 11.3 or earlier and persisting through 12.0 or later
[CASE:4352435] and [CASE:4354378]
In Mathematica 11.3 and 12.0,
...
0
votes
0answers
35 views
making replacements when patterns don't match exactly
I want to simplified some mathematical expressions, and they are similar to
...
7
votes
1answer
101 views
Partitioning a list by cumulated sum when the accumulate reaches a fixed value
I have a list dat = {10, 10, 10, 10, 10, 40} .
When the cumulative sum of dat reaches >=...
1
vote
1answer
46 views
TagSetDelayed for spotting zero derivatives
I am trying to implement my own differential operator, d[arg_, var_],
that computes the derivative of arg w.r.t. ...
7
votes
3answers
244 views
Faster way to solve android lock valid patterns
With the password grid shown in the Android home screen, how many valid passwords are possible?
The rules for creating a pattern is as follows.
We must use four nodes or more to make a pattern at ...
2
votes
1answer
59 views
Pattern matches Sin but not Exp? [closed]
I want to write a pattern that matches unary functions applied to a certain head named dual, used in replacement rules like this:
...
2
votes
0answers
25 views
Pattern matching and NonCommutativeMultiply
I am trying to define some functions using NonCommutativeMultiply and I am experiencing some strange behavior.
Consider the following expression
...
2
votes
2answers
65 views
Triangular matrices with conditions
I would like to generate a lower triangular matrix that has checkmarks in the non-zero entries. The way that I created this matrix is the following
...
2
votes
1answer
32 views
Removing all sublists containing any arbitrary string as one or more of its list component
so, basically I have a list of sublists of varying length. For example,
...
8
votes
3answers
247 views
How can I check if a function can be written as $a * \sin (b * x + c) + d$?
I want to write a function that takes another function, say $f(x)$ and a variable $x$ as input and return True it this function can be written in the form ...
13
votes
6answers
635 views
Replace zeros in a list with last nonzero value
This question is closely related to the problem of zero crossings.
Suppose I have a list l = {-1, -1, 0, 1, 0, 0, -1, -1, 1, 1, 1, 0, 0, 0, -1}
and I want to replace the zeros with the previous ...
6
votes
1answer
216 views
The differences amongst f[x_], f[x__], and f[x___] [closed]
This is probably very elementary but I have not used the following and I cannot find anything online, and I was unable to find something here.
Can someone explain to me the differences amongst
<...
0
votes
0answers
22 views
Check whether the argument of a function is a matrix with numerical values
I know that
MatrixQ[expr,NumericQ]
tells whether expr is a matrix with numerical values or not.
How do I implement such a ...
1
vote
1answer
35 views
1
vote
0answers
34 views
Replacing factors that are only dependent on a single specific variable
I have expressions with terms that are products of factors. Some of the factors are expressions that depend on a single specific variable. I would like to replace those factors with constants and ...
1
vote
0answers
64 views
Graph of a list of rules with coefficient
I am trying to transform an expression to a list of rules and after that plot its graph. The expression has the following form
...
8
votes
2answers
432 views
A simple problem about a Rule example
The documentation says that "Rule represents a rule that transforms lhs to rhs" and gives the following example:
...
0
votes
2answers
49 views
Monte Carlo Method [duplicate]
How do you use a Monte Carlo method to approximate the area enclosed by the circle.
2
votes
0answers
72 views
Lambda calculus reduction in Mathematica
Are there any built-in functions for reducing lambda terms in Mathematica? If not, how might one do it? I've heard of Function, which is good for $\beta$-reduction, ...
7
votes
3answers
151 views
Creating rule-based sublists
I have a list each element of which consists of a list containing two strings and two integers:
...
2
votes
1answer
39 views
Replace sub-expressions matching a pattern unless located under specific heads
Suppose I have some rule, e.g. Re[x_] :> (x + Conjugate[x])/2. I want to apply it to all matching sub-expressions in some expression, excluding any sub-...
3
votes
3answers
77 views
Identify complex expression and replace
I'm having trouble finding a way (if there is) to analyse an expression, identify a complex pattern in it and then replace it with another thing. I think it will be easier to explain my problem with ...
6
votes
0answers
67 views
Repeated string pattern: difference between the FrontEnd and WolframScript?
This code works fine in a string based interface like WolframScript or Mathematica Kernel.
Run this through a string based interface
...
2
votes
2answers
88 views
DeleteCases pattern which applies Chop to all elements
In my current macro, I have:
DeleteCases[Chop[FullSimplify[RowReduce[something]]], {0 ..}]
This works fine for both, exact and numeric complex numbers (with ...
0
votes
0answers
26 views
Why are unrelated symbols localized in Module? [duplicate]
As I understand, an expression like Module[{var},expr[var]] localizes var and evaluates ...
9
votes
1answer
94 views
Pattern matcher behavior change in 11.3
When trying to switch from version 10.3 to 11.3 I noticed that some of my code do not work properly. After some investigation I found that the problem is with pattern matcher. Here is the example:
<...
7
votes
1answer
117 views
Using PatternSequence and __ / Repeated[]
I'm trying to scrape this Wikipedia page ('Deaths in 2019- July', I'm writing this on the 14th.). I am failing miserably and I'm starting to think that it is due to some misconception on my part on ...
1
vote
1answer
43 views
Respecting excluded index in sum
I'm using a function involving a sum where some indices are excluded:
...
4
votes
1answer
60 views
Pattern of nested functions
Suppose I have a list of elements
list = {f[b[G[1]]],f[b[1]],k[k[k[G[1]]]]}
What is the pattern associated to an expression in which the function ...
1
vote
0answers
22 views
Count does not count NumberString directly [duplicate]
I want to count all NumberStrings in a list:
In[1]:= myList = {"123", "456", "789", "ab1", "cd2", "xyz"};
but, surprising (to ...
2
votes
1answer
47 views
Unconstrained pattern evaluated by a constrained replacement rule
I'm working with a notebook that defines NonCommutativeMultiply on a defined set of symbols, called operators. Semantically, ...
1
vote
2answers
60 views
Find and replace particular multiplication of factors in big multiplication
I have a sum of terms where each is a multiplication of several factors. For example my expression in FullForm is
...
3
votes
3answers
99 views
Find element in a list matching a pattern (using wildcards)
Somehow, I did not manage to find anything related to that.
Suppose, in my Global list of variables, I would like to make a search such that I obtain all the ...
2
votes
1answer
31 views
Setting default function values for particular option values
I have a function with some optional arguments. How do I assign a value for the function when one of the optional arguments takes a particular value, regardless of any other argument values?
0
votes
1answer
47 views
Pattern ReplaceAll warning
Why does the following code give me a warning, but then still work?
a1={{1,2},{3,1}}
a2={"foo","bar"}
a1/.{x_Integer,y_Integer}->{x,a2[[y]]}
After a "Part: ...
1
vote
2answers
74 views
How to use KeyValuePattern with individual replacement rules?
What's the syntax to use individual replacement rules for key-value patterns?
This returns only the first match:
...
4
votes
0answers
70 views
Why does Shortest not work inside SequencePosition?
Why does Shortest not work in a SequencePosition call? The following two commands return the same answer:
...
4
votes
1answer
64 views
Pattern matching repeated arguments of Times
I am trying to match against products of elements with a specific pattern. Since a product of symbols A B C is just Times[A,B,C],...
5
votes
1answer
111 views
DeleteCases using two lists but with partial match?
I searched and tried different solutions on SE but nothing worked.
I have two lists and would like to remove items from list1 that have a PARTIAL match with items ...
4
votes
1answer
142 views
Pattern test: _Integer vs _?IntegerQ [closed]
While checking out the different pattern replacement methods in this question, I have a query regarding the basic difference between the following two replacements:
...
1
vote
1answer
293 views
Replacement using pattern matching?
Starting with the expression
eq1 = 5 Exp[1 + 2 x + 3 x^2 + 4 x^3];
I want to implement the following transformation:
...
0
votes
3answers
43 views
Select elements from nested list where one element is largest
I'm trying to speed up the following, but implementing efficient pattern matching isn't intuitive to me yet, even with lots of examples.
I have a list of ((x1,y1,z1), (x2,y2,z2)) pairs, and I want to ...
2
votes
1answer
67 views
Pattern matching failed [closed]
I want to replace Θ[z + m τ] by a[m] Θ[z]. So I consider the pattern ...
1
vote
2answers
76 views
Function returning a pattern with condition - how to prevent condition to evaluate prematurely?
I figured it would be convenient to have a function
that returns a pattern, that match equally nested brackets, of the specified type. Such a pattern is easy to create, but I get some error messages, ...
3
votes
2answers
83 views
Using DeleteCases with a defined function with two arguments as a pattern
I am trying to manipulate some large datasets in Mathematica. I have plotted the data, and I would like to be able to easily remove points from the dataset, and it's fairly easy to identify the x-...
4
votes
3answers
87 views
Composition of polymorphic functions
Using pattern matching one can easily create polymorphic functions in Mathematica
f[{a_, b_}] := {a^2, b^2};
f[c_Integer] := c^4;
Now I want to create another ...
