Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,125
questions
2
votes
1answer
23 views
How to substitute an expression in side a particular head or inside a particular pattern?
Let say I have any expression
ex= f[h[r[x y]]] g[x z]
and I want to replace the x with w, ...
10
votes
3answers
694 views
How to NOT a specific pattern?
been going around in cirlces on this:
{1/3, 1, 0.22, 3, "v", 4} /. _?NumericQ -> "999"
Now I'm trying to replace everything that is not a ...
10
votes
2answers
216 views
i_:0|1 varies in v12.1: incompatible change or bug?
Just check
i_: 0 | 1 // FullForm
In v12.0 or earlier the output is
Alternatives[Optional[Pattern[i, Blank[]], 0], 1]
But in ...
0
votes
0answers
30 views
Matching sum of negative terms with a pattern [closed]
Consider a really, really simple expression:
test = (-x - y);
The FullForm of test is ...
5
votes
2answers
272 views
Why association pattern unmatched when using variable
I have association and want to replace integer in specific element in this association. I'm trying to build pattern to be used by ReplaceAll command. When number is ...
4
votes
1answer
47 views
Name of patterns cast as expressions from strings
I'm trying to match a part of a string while imposing conditions on the patterns, e.g.:
StringCases["223", a: DigitCharacter ~~ b: DigitCharacter /; Unequal[a, b]]
...
4
votes
1answer
240 views
What does Sequence[2,4]^2 mean?
I am learning pattern matching. An example that confuse me is as follows.
Foo[x__?EvenQ] := x^2;
Foo[2, 4]
which is equal to ...
1
vote
1answer
38 views
ReplaceAll with pattern matching not working with list of lists
Abstract This is just a learning exercise for me. I am trying to create a function that will take a list of vectors, multiply them by a constant if constant is given, and then add all vectors. If we ...
2
votes
1answer
50 views
Write repeated expressions within a rule more simply
Is it possible to shorten the length of a (delayed) rule (i.e. lhs :> rhs) when there are expressions which repeat several times? Those expressions involve ...
2
votes
1answer
39 views
1
vote
1answer
58 views
Matching Polygons in a list of Polygons
In the process of creating a more complex algorithm, I've stumbled upon some strange behaviour I am trying to understand with my matching function.
What I'm expecting to see on the right hand side is ...
3
votes
2answers
39 views
Replacement rules which for elements of a vector which meet conditions
I'm trying to create a function which will replace elements of a list with their values modulo 1, i.e. Mod[x,1], but only if ...
0
votes
1answer
31 views
using pattern matching to separate coefficients and functions
I want to find out the coefficients and functions from an expression and possibly save them in separate files with same order.
I have the following toy example:
...
-1
votes
1answer
47 views
Function matching any head (Example: h_[_,_] := 5)
I want to define a function matching any expression with 2 parameters. For example:
_[_, _] := 5
I get the following error:
SetDelayed::nosym: "[,_] does not ...
6
votes
3answers
189 views
replacing a sub-partition (unordered list; multiset)
I am working on a bijection for integer partitions and would appreciate help with two steps.
First, I want to replace each occurrence of (4, 2, 1, 1) with (3, 3, 2). One complication is that the 4, 2,...
4
votes
1answer
90 views
A pattern replacement to force Mathematica to replace inexact 0 multiplication by zero
Hi Consider the following expression which contains multiplication by inexact 0
...
6
votes
2answers
115 views
How to extract all possible sub-products which match specific pattern?
I have an expression of the form
expr = 3*(a.b)*(c.d)*f[x] + 5*(m.n)*(p.q)*(r.s)*f[y]
and want to extract all possible subexpressions matching the pattern ...
0
votes
1answer
30 views
A problem with Cases and Pattern recognition: unexpected behavior
I need the following command (to isolate exponents and variables):
F[X_] := Cases[ X , G[x_]^m0_. -> {x, m0}]
This example gives the correct answer:
...
3
votes
1answer
53 views
Matching symbols in assignments using NotebookImport
How can symbols from assignments, ie left hand side in expressions Set and SetDelayed be matched after importing using ...
5
votes
3answers
233 views
Replacing all subsequences in a list
How do I replace all occurrences of -1,1 with 0,1 in a list
example:
list = {-1, 1, -1, 1, 1, 1, -1, -1, -1, 1}
desired output:
...
10
votes
1answer
221 views
How to clear all definitions matching f[1, …] but not f[2, …]?
I would like to clear all definitions of the form f[1,...] in such a way that f[2,...] remain unaffected.
The two methods I know ...
8
votes
1answer
550 views
Why does Mathematica ignore 1 as an exponent? Or as a coefficient?
Two different examples of same problem:
In: Cases[{f^2, g^3, k^p, h}, x_^n_ -> n]
Out: {2,3,p} # The result misses the ...
2
votes
1answer
44 views
No need to use Alternatives to construct alternative string patterns?
I am trying to match a list of strings with a pattern, in which there are several possibilities for the characters to be matched. To me, the following looks the most natural way:
...
0
votes
1answer
58 views
Strange behaviour of Cases and pattern matching [closed]
I have encountered a strange pattern matching behaviour which I cannot explain even after going through manual again.
Why does the second line in the code yield different result? Is it a feature of ...
2
votes
1answer
37 views
Why does ReplaceRepeated work differently in numerator and denominator?
I'm confused about the behavior of ReplaceRepeated.
ReplaceRepeated[a Sqrt[b], Sqrt[b] -> c] gives the expected (* a c *), ...
2
votes
1answer
35 views
Remove parentheses in a List
I want the output to be: a,b when the input is {a,b} . How do I do this please? Flatten command does not work.
1
vote
1answer
50 views
Attributes for private functions
I am not sure if what I want to do can be done, but I thought to ask anyway.
Note: I already have in hand a workaround, I was just wondering for the power/simplicity that Mathematica may provide.
...
2
votes
1answer
22 views
Is there a better way to “ Select non self mapping elements from a list of rules”?
Is there a better way to get the non self mapping list of rules from the list of rules
abc = {a -> a, b -> c, d -> d, e -> f};
To
...
0
votes
0answers
16 views
Do named patterns inside Except work inside OrderlessPatternSequence?
This works:
f[{x, a, b}, {y, c, d}] /.
f[{sgn1_, _, _}, {Except[sgn1_, sgn2_], _, _}] :> matched[sgn1, sgn2]
(*matched[x,y]*)
This doesn't match:
...
6
votes
1answer
72 views
How to use match and blank
This very basic problem baffles me. From the documentation I do not understand the results of
...
0
votes
0answers
26 views
Construct string pattern for two different types of lines
I need to increase my understanding of string patterns. My specific problem is that I have a definition of a type in SystemVerilog that has lines that are either single-bit or multi-bit. I want the ...
2
votes
1answer
42 views
Pattern to match any differential of a certain variable
I'm trying to come up with a pattern or just implement a function DifferentialEquationQ so I can have another function assume different behaviour when it's input is ...
0
votes
0answers
13 views
How to insert partitions into a list to make it match the partitioning structure of another list [duplicate]
I have two lists with the same number of elements at the bottom level:
list1 = {a, b, c, d, e, f, g, h, i, j};
list2 = {{1, 2, 3, 4}, {5, 6}, {7}, {8, 9, 10}}.
I need to insert partitions into list1 ...
0
votes
2answers
53 views
Pattern matching for products of variables [closed]
What I am trying to do is very simple: In an expression that is polynomial in x,y, I want to check if there are products of the form ...
0
votes
4answers
58 views
Match & replace the elements in a dataset
somewhat similarly to Replace Elements in a Dataset by rules, I'd like to replace the components in all columns named "microseconds" in a hierarchical dataset, with their respective quantity.
...
2
votes
1answer
38 views
Find minimal recoding of the (symbolic) entries of an $8 \times 8$ matrix
I have the following $8 \times 8$ matrix
...
0
votes
0answers
46 views
How to use DeleteCases to delete table entries with lists of strings longer than one character?
I'm currently looking at using Mathematica to perform sequence alignment on around 4000 sets of genomic data. I've been going about this by first isolating nucleotide sequences for the protein I need, ...
2
votes
1answer
47 views
How to match a pattern with exact occurence?
Maybe the way I expressed is not very accurate, but a very simple example will help to understand the question:
For
Subscript[a,i]+Subscript[a,j]**Subscript[a,k]
...
0
votes
0answers
25 views
Pattern matching on derivatives
I want to manipulate and do pattern matching on sequences of functions and their derivatives, but I'm struggling to work with the multiple indexing required. Here is an example. Let
$$
y(z) = \sum_{j=...
5
votes
0answers
53 views
Can't seem to match multiple KeyValuePatterns in one pattern
Let's define a couple patterns that we can use to match Associations.
...
1
vote
1answer
26 views
Multiplying two expressions with a specific function, efficiently
Paraphrasing, the problem I am trying to solve is the following. I am given two "matrix valued" sums
...
4
votes
2answers
35 views
RandomVariate on multidimensional Bernoulli array
Executing...
Map[RandomVariate, Map[BernoulliDistribution, RandomReal[1, 5]]]
yields the expected result, e.g. ...
3
votes
1answer
103 views
How to use patterns to specify variable type as Boolean (True, False) in analogy to x_Integer, x_Real, x_Complex, x_List, etc
Say I define a function f[x_, y_]:= ..., the concrete definition of which is not important now.
What is important though is, that I want ...
3
votes
1answer
90 views
DeleteCases with a case as float?
Might the DeleteCases have issues in matching when the list is of floats (machine precision numbers)? E.g. in this code it might fail to match correctly because ...
1
vote
0answers
36 views
Apply SequenceReplace with a fixed shift
How can I apply SequenceReplace with a fixed prespecified shift instead of a shift equal to the length of the pattern, on a given list? E.g. ...
6
votes
5answers
189 views
3
votes
1answer
52 views
Naming repeated patterns
How can I name a repeated pattern to apply a rule on it?
In the example below I have two element sequence. There is no problem in naming them and then applying some function on it:
...
7
votes
2answers
90 views
How to use ExtractArchive[] with a pattern that does NOT match
ExtractArchive has the ability to Extract all files that match a pattern. For example this will extract all the JPEG files from the archive:
...
3
votes
2answers
62 views
Setting nested optional argument with a default when unpacking from a given Head
I have a head that holds a single argument, and I want to unpack the value inside it while also assigning a symbol to the value itself, for example:
...
4
votes
2answers
125 views
How to apply Cases on multiple parts of sublists?
I have the following data
sol={{2063, 853}, {2066, 855}, {2069, 857}, {2072, 859}}
I can find prime-pairs by
...
