Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,297
questions
2
votes
0answers
45 views
pattern test on position
At the moment I'm using something like this to get the positions of entries of a matrix satisfying a specific value:
...
4
votes
3answers
152 views
Permutation avoidance function
It is common for me to see if a permutation of 1,2,...,n, avoids some fixed permutation pattern. For example, the permutation [1,4,2,3,5]
contains the pattern 1,3,2, as the elements [1,4,3] appear in ...
5
votes
1answer
89 views
Patterns are not Sequences are not Lists, or: Global Function Argument Reversal
H[z_] := z /. {F[p__] -> F[Reverse[p]]}
F[{x, y}] + F[{x, z}] + F[{}] // H
Almost. It gives an annoying "Nonatomic Reverse" error message at the ...
1
vote
0answers
24 views
N on equation with numbered variables [duplicate]
Say I have a system of polynomial equations in the variables x[1],...,x[n]. Sometimes want to make such equations numerical (as in: the coefficients become floats) ...
3
votes
1answer
128 views
Why the two outputs are different?
My first code is {a, b, b, a, b, a, b, a, a, b} /. {___, x : Longest[PatternSequence[a, b] ..], ___} :> {x} and its output is {a,b,a,b}.
The second code is ...
2
votes
2answers
81 views
Equality of expressions with different variable names
I have some multivariate systems of expressions that I want to check for equality up to allowing relabelling of the variables. For example the two expressions below would be the same:
...
1
vote
1answer
68 views
why combining 2 patterns in Alternatives in Cases do not give same output as when each pattern is used separately?
Given expression
expr = y'[x]^3 + y'[x]*Log[y[x]*y'[x]^2] + y'[x]^(1/2) + x/y'[x]^7
$$y'(x)^3+\sqrt{y'(x)}+\frac{x}{y'(x)^7}+y'(x) \log \left(y(x) y'(x)^2\right)$$
...
0
votes
1answer
38 views
Formatting expressions with numeric exponents using pattern matching
Thank you all in advance.
Question:
I want to change the format of this expression (n + r)^3/n^3 into this (1+r/n)^3using rules ...
3
votes
2answers
277 views
How to extract email addresses from a text file using Mathematica
I have a text file which I have uploaded here. I want to find all email addresses in this text file. I just know that some of them are after "Subscription Date" expression (I don't know if ...
2
votes
1answer
82 views
Mathematica does not recognize pattern when changing by numerical values
The following returns False:
MatchQ[(-1 + (1 + E^-x)^0.1 )/(1 + E^-x)^0.2, ((1 + Exp[-x_])^v_. - 1)/(1 + Exp[-x_])^u_.]
False
And the following returns True:
<...
1
vote
1answer
46 views
How to create a simple transformation function on lists using short form of ReplaceAll?
I can easily do this with Map so the real goal of this exercise is to get a better grip on using transformation rules. Please help with this. The outputs should be ...
0
votes
1answer
36 views
Converting parts of some string into another notation
I have a big string of data and most of them are in the form Name = number^{number}_{-number}, some are in the form Name = number \pm number. I what to convert the latter into the notation.
For a ...
0
votes
1answer
98 views
Matching a Dynamic Argument Pattern
times is a list of times i.e. matching {{hour_, min_, sec_Real}..}.
I want to call ...
2
votes
0answers
36 views
Can't match custom head in function signature [closed]
I have written a financial charting function which has the following signature;
...
4
votes
0answers
52 views
Pattern matching at multiple levels [closed]
Pattern matching is my favorite feature. Is it possible to destructure a symbol but still refer to the whole symbol? I mean something like (this won't work of course)
...
3
votes
1answer
31 views
Removing conditions on patterns from LHS of a rule
Let's consider a rule which takes conditions on the patterns specified on the LHS:
In[1]:= rule = j[n1_?NonPositive,n2_?Positive,n3_?Positive]:>AAA
I would like ...
7
votes
1answer
189 views
How to set deeper patterns in arguments within function definitions. For example if an argument must be a list of 1 or more strings
Suppose I want to define a function whose argument must be a List of only Strings and List must have at least one member. I know how to require that the Head must be a List but how does one qualify ...
0
votes
0answers
41 views
Define multivariate even general function
I want to define a multivariate even function. This question shows how to do it for a single variable function Defining general odd function but I don't see how to generalize the syntax to multiple ...
3
votes
2answers
154 views
How not to Simplify square roots
Given
t1 = {1/7 (4 + Sqrt[37]), 1/15 (3 + 2 Sqrt[7]), 1/2 (5 + 3 Sqrt[2])}
I do not want to simplify the square roots. I want to get
...
2
votes
0answers
43 views
'Cases' command does not recognize specified patterns
I am having a problem with the "Cases" command. If I execute the following code
...
0
votes
0answers
50 views
Derivative with respect to function of any argument
I have the expression
L = v1[k1] * M[k1, k2] * v2[k2].
v1, M, and ...
3
votes
0answers
71 views
Association vs Pattern Matching: which one is better for data storage?
Say I have a few key-value pairs. I can store them with Association as
...
2
votes
2answers
68 views
Cutting of terms on denominators of giant expression
I have an immense expression of the form
$$
\sum_i \frac{f_i(X,Y,x,y)}{(a_iX^2+b_iY^2+c_ix^2+d_iy^2)(e_iX^2+g_iY^2+h_ix^2+k_iy^2)},
$$
where at $a_i$ or $b_i$ AND $e_i$ or $g_i$ is different from zero....
2
votes
1answer
135 views
1
vote
2answers
67 views
How to construct a pattern that match the multiple partial differential of any multi-variable functions?
For example,I want to match a multiple partial derivative of a function $f^{(1,0,1)}[x,y,z]$ which is the same as$\frac{\partial^2{f}}{\partial{x}\partial{z}}$.The only information given is the list ...
1
vote
1answer
45 views
How to make a vector of elements the pattern of a function?
if I have an expression that contains a lot of symbolic elements and I would want to make it a function of the vector containing all the elements I've found a solution based on rule delayed:
...
5
votes
2answers
211 views
using StringReplace and StringPattern to convert exp(...) to Exp[....]
I am looking at a file generated by another CAS. I'd like to convert it to Mathematica syntax.
Only issue is how to convert exp(....) to ...
1
vote
0answers
88 views
How to make a function ignore an argument [closed]
Motivation
I am trying to call a function f, that has either 1 or 2 (or multiple) parameters, from a function g that uses ...
7
votes
1answer
138 views
Fill in the StringBlank
I have a string that has blanks marked by a marker; (in this case, an underscore):
"f_ath_r".
I can execute the following command to get the word.
...
3
votes
2answers
100 views
Built-in functions on the LHS won't pattern-match
I have this pattern-matching problem:
F[X_,myminus[X_]]:=0
F[1,myminus[1]]
Works.
...
0
votes
1answer
54 views
How to write a pattern that matches all linear combinations of functions involved except 0?
I am trying to write the simplest (and efficient) pattern that matches the linear combination of all functions except when the combination produces zero?
Consider the following as an example:
...
3
votes
0answers
45 views
Preventing $-renaming of pattern names in lexically-scoped constructs
When you use a lexically-scoped construct like With or Function to perform replacements in an expression, Mathematica might ...
1
vote
1answer
37 views
user-defined functions and "pattern" being returned [closed]
I define a function as
f[J_] := Exp[J^2/2\[Mu]]
but when I try to taylor expand as
k[J_] = Series[f[J] ,{J,0,2}]
I'm getting ...
2
votes
0answers
50 views
7
votes
0answers
65 views
Why does Longest not work on OptionsPattern?
When having a function with optional arguments and options, I frequently find myself writing something like this:
...
2
votes
1answer
46 views
Is there a way to extract a sub pattern from a repeated PatternSequence?
Consider the following Pattern expression:
...
9
votes
2answers
239 views
Pattern matching product with arbitrary number of terms
I am trying to write a function to convert an expression of the form
$$\alpha x_1^{n_1} x_2^{n_2} ... x_N^{n_N}$$
(with some coefficient $\alpha\in\mathbb{R}$) into a list of indices and powers
$$\{\{...
3
votes
1answer
77 views
Pattern matching problems involving FullForm and Plus and Times
I am trying to match an expression that will be a sum of more than one terms, with the last one being a product. For example, the objecta+b+x*y. I am using the ...
4
votes
1answer
116 views
Alternatives in pure function construction
When I declare a function f in the following form:
f[a|b] := 1
then I can use it like:
...
0
votes
0answers
32 views
Issues in expanding expressions with formal sums
I have a very long expression involving formal sums to infinity, unfixed functions and several variables.
In this very long expression, I need a typical term, like
$\frac{6 A \sigma \sum _{n=0}^{\...
0
votes
0answers
26 views
How to rearrange terms in an expression to a particular form (e.g. A/w-> A*(1/w)
I have a huge expression for which the numerators are a big mess, involving numbers, variables, formal sums and unevaluted function, let's call the numerators Ai, with i=1,2,...n
This "beast"...
3
votes
1answer
42 views
Type formation rules for 1-position expressions
I made a summary of the rules for formation of types for simple 1-position expressions, as I understand them.
Here it is in textual form:
A symbol, say, α, is a discrete entity, represented by a ...
2
votes
0answers
39 views
What sorts of expressions can be Solve'd for?
We can Solve for expressions that match _Symbol, as in Solve[x^2+1 == 0, x]—but we can also ...
1
vote
1answer
54 views
Defining a two-variable function with a parity property
I would like to define a function that has the following property $f(-x,y)=f(x,-y)$.
An example is $f(x,y)=x y$. For simple inputs, I can impose this easily enough as:
...
3
votes
1answer
65 views
How to Map over a BlankSequence? [closed]
I would like to replace any function f[x, y, ...] in a certain expression with the same function with all its arguments squared, i.e. ...
3
votes
1answer
70 views
How to do context-sensitive matching with the pattern system?
In Perl RegEx, we have the look-ahead/behind feature; it there a similar functionality available for Wolfram Language patterns?
Re @mikado:
Suppose we have a random expression in ...
4
votes
1answer
77 views
SequenceSplit around empty sequences is inconsistent
Bug introduced in 11.3 and persisting through 12.3
Only the first one recognizes a zero-length sequence between non-X's.
...
0
votes
1answer
61 views
Finding a mapping between two types of (generalized) hypergeometric series
I am given two functions, one is of the form $2F1(a,b,c;z)$, where $2F1$ is a hypergeometric series. The other one is a generalized hypergeometric series $3F2(d,e,f;g,h;w)$, where the characters are ...
1
vote
3answers
38 views
How can I let StringPosition consolidate overlapping matches?
Consider an example like this one:
StringPosition[" -aa.ef -ag.hi -aa.ei",
RegularExpression["\\s+-(?=a+\\.)"]]
which returns
...
3
votes
1answer
63 views
How can I let RegularExpression remove all colors from its regex-input string before processing it?
Regular expressions are a very powerful tool, but such expressions are often very cryptic. If you want to understand them, it is best to have colored pencils at hand to color-code the parts that ...