Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
1,339
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Terms of expressions with non-commutative multiplication that meet the given criteria
There is the following expression:
expr=a^3**x**Transpose[x]**y+x+y**Transpose[y]**x**a^3+x**Transpose[y]
It is necessary to apply the ...
- 1,626
3
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2
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810
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How can a verbal reasoning question be solved with Mathematica?
Could a "verbal reasoning" problem like the following be solved with Mathematica? What comes next in the series.
KD XP NG VN QJ TL TM
Correct answer is <...
- 157
3
votes
3
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137
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Deleting sublists where an element repeats beyond a repetition threshold
I am looking for some help constructing a function Part[M_,N_] which outputs the list of all integer partitions of positive integers up to $M$ such that in each ...
- 1,287
3
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2
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150
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StringReplace question from "An Elementary Introduction to the Wolfram Language"
I'm unable to come up with a solution to the following question in the "Introduction" online book, Chapter 42:
"42.6 Make any 2-letter word uppercase in the first sentence from the ...
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1
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1
answer
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How to make a pattern that matches only when one of the argument's Head is a Plus?
I am trying to set up rules as follows:
ClearAll[CircleTimes];
If the arguments are the same the output is zero:
...
- 8,105
4
votes
1
answer
68
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Replacement, PatternTest, Module related Question
Let's see how MMA handles following type of expression :
Replace[L, {pattTest1->rhs1, pattTest2->rhs2, pattTest3->rhs3}, {1}]
Specific example :
...
- 2,451
2
votes
1
answer
117
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Pattern match with "+" sign
Can you pattern match with a "+" sign?
Here is the recursion...(which does not work)
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- 341
1
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0
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71
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sometimes Select / sometimes Position is faster
As you see,
For list L,
L1(Select method) is slower than L2(Position method).
But for list <...
- 2,451
1
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0
answers
50
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Pattern matching and polluting the namespace
I am building a library. Inside of BeginPackage environment there is a function
...
- 74
1
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0
answers
23
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TreePosition with multiple (not just node data) conditions
Given a Tree object, TreePosition takes patterns only on the "data" of the node plus a level spec.
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- 3,720
0
votes
0
answers
36
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Extracting function domain from a finite set of assignments
Suppose we define a function through a finite collection of equalities, e.g.,
f[1] = 1; f[26] = 321
and so on. We can extract the set of output values by running
<...
- 595
6
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4
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545
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7
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3
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252
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Removed all undefined from a list of rules
My output from NSolve is a list of rules, most of these are undefined, I want to remove those rules.
More specifically I have a list
...
- 305
0
votes
1
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26
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Confusing abnormalities observed when counting a specific operator in an expression [duplicate]
Recently I have met with some confusing abnormalities when trying to determine if there is a specific operator (usually Plus[] ) in an expression by programming. ...
- 289
0
votes
1
answer
77
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Symbol for "anything" [closed]
Is there a way to use in Mathematica something like "anything" symbol to simplify symbolic expressions?
Exemplary, I would like to denote with "B[*]" B[t] for arbitrary parameter t....
- 625
8
votes
3
answers
486
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Replace 'n'-th occurence with number 'n'
How can I replace n-th occurence with number n for string/for list?
For string :
...
- 2,451
1
vote
1
answer
66
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The replacement operator -> and :> and pattern
I'm confused by the difference between two replacement operators -> and :>, and their relation with the dummy variable (...
- 381
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3
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399
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How can I change the expression x1 to x[1] in a simple way?
I have one expression,
exp0=x1+x9/8+ x4 x5
I want to get
exp1=x[1]+x[9]/8+x[4] x[5]
Is there a very simple way to do that?
- 1,217
5
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1
answer
54
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Picking integer compositions with certain descent patterns
I am trying to find a nice way to pick out all the integer compositions (ordered partitions) of an integer $n$ that satisfy a given pattern of descents between some adjacent elements. Writing a ...
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56
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How to make a replacement rule matching exponents including 0 and 1
==============Edit for solution(s):
For anybody who does not need to worry about the structure of any coefficents and has non-negative powers this solution from @kirma works very well:
...
- 21
2
votes
1
answer
104
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How do I locate non-numbers
If I have a list containing both numbers and non-numbers, such as
{1,2,3,4,5,6p6,7p7,8,9}
how do I locate the positions in the list which do not contain numbers. ...
- 755
4
votes
1
answer
74
views
Substitute function back into solution
I have a expression
G[x] := (1-x^2)(1+A*x)(1-a*x)
where $(a,A) \in \mathbb{R} $.
Now this heavily simplifies some other expression. But these expression are no ...
- 305
3
votes
2
answers
291
views
How to define a function in Mathematica without overriding the previous definition?
I'm a beginner at Mathematica and trying to define a function for the Collatz conjecture, and here is my code:
...
- 41
7
votes
3
answers
199
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Select pattern at the list sub-level
I want to get a list from a parent list (containing sub-lists of unequal length) using Cases and a matching pattern. The parent list is
...
- 973
1
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1
answer
51
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Why this pattern can't be matched? [closed]
My code is {x,y,z}/.PatternSequence[x,y]->t.I think the answer is {t,z},while the output is still ...
- 71
3
votes
1
answer
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Is there any particularity of Sum/Product in replacement
Here is an simple replacement:
Log[x[k]] /. Log[a_] -> a*xbar
I get the answer in my mind:
xbar x[k]
Similarly, I use ...
- 31
0
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0
answers
36
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Evaluate derivative after replacement?
I am trying to implement a simple integration by parts on functions with zero boundary conditions. For example, I currently have something like
...
3
votes
1
answer
213
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Pattern matching with two variables - derivatives on 4-vectors
I am interested in pattern matching with two variables and not just one, and more specifically implementing derivatives on 4-vectors. In the case of interest the 4-vectors have two indices; one is in ...
- 4,113
7
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2
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195
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Dividing a list into $n$ non-overlapping pieces?
Is there a function that gives all the ways a list can be divided into a specified number of non-overlapping pieces, where the order is maintained?
I can do this with ...
- 3,446
3
votes
3
answers
89
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Regular Expressions in FileNameJoin[]
I'm attempting to create a list of folders that match a particular pattern.
For example, consider I have the following files in a directory structure:
...
- 177
2
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3
answers
104
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Selecting patterns
I have data as a list of four element lists, some with missing data, thus
...
- 579
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1
answer
43
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weird behavior in pattern-matching and condition
I'm confused by the following three different results involving pattern matching and condition.
...
- 381
7
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1
answer
160
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A uniform rule for matching numeric and symbolic expressions for inverse of complex numbers?
I am trying to do some substitution on the basis of pattern matching. I am trying to replace $\frac{1}{a+i b}\to\frac{a-ib}{a^2+b^2}$ in the following way,
...
- 419
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43
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Convert complex exponential to real exponentials, sines and cosines
While taking the inverse Laplace transform of certain expressions, Mathematica yields complex exponentials. For example, using the following code:
...
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I understand mol but meet difficulty in understanding how `pdetoode` atumatically generate pde-to-ode-rules by using this strange pattern and rule?
I often solve pdes for my research, and years ago I found pdetoode in this forum is very handy. Although it is a small piece of code, it solves several interesting ...
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3
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152
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Finding the index of certain strings in a list
I'm actually using a dataset of much greater dimensions and length but I simplified my problem of string patterns in order to ask this question.
...
- 1,024
4
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1
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98
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Search speed of downvalues when indexing with strings
I'm writing a lot of print functions for different parts in a package and at the moment am using something like
myprint[ identifierString_String ][ data_ ] := ...
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75
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How to test for arguments for a pattern that is of a positive Integer OR Infinity so that both filter through to the definition on RHS?
How can I filter an argument of a function so that definition works on positive Integers (y >= 0) or Infinity? It will ...
- 1,787
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54
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How to specify complicated patterns in function arguments?
Unfortunately, I have not found in documentation how to create complicated patterns in arguments of a function
Consider a toy example. Say, I would like to have a simple function
...
- 664
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55
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Store pattern names in variables, and use them in Condition (/;)
I am trying to create patterns whose form is not hard-coded, and which are not explicitly directly written. For that I want to use one list of pattern names to name some parts of a ...
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How do I modify all the list elements as patterns
Is there any easier way to change all the list elements as elements with patterns?
Here is an example:
list={a,b,c,d}
I want to transform it as a list of patterns ...
- 973
3
votes
3
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Encode expression into a list
I have an expression of the form:
$$c {\partial^{k+l} \Phi(\theta,\phi,n) \over \partial \theta^k \partial \phi^l}$$
$n,k,l$ are (positive) integers. $c$ is some constant. It is also possible that $c$ ...
- 951
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0
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49
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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:
...
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3
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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 ...
- 2,292
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1
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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 ...
- 887
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0
answers
26
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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) ...
- 928
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1
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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 ...
- 71
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2
answers
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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:
...
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1
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1
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77
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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
$$y'(x)^3+\sqrt{y'(x)}+\frac{x}{y'(x)^7}+y'(x) \log \left(y(x) y'(x)^2\right)$$
...
- 108k
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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 ...
- 93