Questions tagged [pattern-matching]
Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.
3
votes
3answers
89 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
29 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
42 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
61 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
61 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
49 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
105 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 ...
3
votes
1answer
128 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
265 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
36 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
64 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
1answer
54 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
69 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-...
3
votes
3answers
68 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 ...
3
votes
1answer
46 views
PatternTest vs Parallelization
Bug introduced in 10.0 or earlier and fixed in 11.2
Consider the following function
...
0
votes
1answer
30 views
Notation package: StringMemberQ in conditional notation definition
Suppose that I have a list, allSpecies, that contain a set of symbols, each of which has been assigned a new notation using Notation[...]. As an example, the internal representation is C60s, and the ...
2
votes
2answers
70 views
Replacing with pattern on built-in symbols?
I have:
f[a, b] /. f[x__] -> g[x, 0] // InputForm
(* Out: g[a, b, 0] *)
Which is what I expect, but when I use a built in symbol instead of ...
0
votes
2answers
194 views
Construct a pattern with an optional head
How can I construct a pattern that matches both f and h[f] without using the symbol f more ...
0
votes
1answer
59 views
Parsing output of a reduce operation
This question is a broader question than this. The output of Reduce can be of different forms. The solutions proposed for that question works well when the output of Reduce is as provided in that ...
2
votes
1answer
70 views
How to trace value assigned to local variable(variables in Module)?
Bug introduced in v10.1 or earlier and persists through v11.3
CASE:4240757
Here is my code:
...
0
votes
1answer
36 views
How to get all the expression with pattern match? [closed]
The FullForm of my equation final(obtained from System Modeler) is:
...
12
votes
0answers
126 views
Orderless breaks pattern match
Bug introduced in 10.3 or earlier and persisting through 12.0.0
10.0.2 is not affected.
I am perplexed by the effect of Orderless on pattern matching. Starting ...
4
votes
2answers
62 views
Identifying total derivatives
I would like to identify which terms in my expression are a total derivative and which ones are not.
For expressions in which all terms are a total derivative, one can simply use integrate to find ...
3
votes
2answers
128 views
Can pattern assumptions be made reliable?
It is possible to use patterns in assumptions such as f[_]>0. This does not seem to be explained in the documentation but is for instance pointed out in Is it ...
4
votes
1answer
101 views
A single argument pattern definition applies to multiple-argument patterns?
Consider defining a pattern rule, such as
myFun[x_]:=x
As far as I understand Mathematica syntax, this rule means
...
1
vote
0answers
90 views
Design completion idea for Position [closed]
This is not exactly a question but rather a suggestion for a design which I think would greatly improve Mathematica. Before I put this to Wolfram Research I would like to see what other people think ...
2
votes
0answers
40 views
Match an expression that has a descendant pattern
I have a complicated expression in which I have another expression p which, when it’s present, I want to match the outer expression and all of its children. I was hoping for something like ...
5
votes
2answers
221 views
Manipulating a general length function
As a minimal example, define a function like s[1,2,3]; this is a function of three arguments in this case, but I'd like to apply this general idea to functions like ...
4
votes
2answers
79 views
Partitioning string into longest substrings of given characters
I want to partition string into longest substrings that each contain only specific characters, beginning from left to right with no overlaps, always choosing the longest one possible at current ...
8
votes
1answer
287 views
Is there a defined priority for pattern matching?
If you define a function g, like so:
g[x_?EvenQ] := "even"
g[x_?NumberQ] := "number"
why will Mathematica always return ...
0
votes
2answers
67 views
How can I extract the parameters from my expression automatically?
I have an expression of this form
$\qquad e^{-x^2b_0+xb_1+b_2}(c_0+c_1x+c_2x^3+c_3x^3+c_4x^4)$
However, it has complicated parameters.
...
5
votes
1answer
146 views
Can someone please explain the code from another question
Source: Position of a pattern-matched part of an expression
Can someone please explain the following code by Leonid Shifrin.
...
5
votes
4answers
92 views
Finding where a specific number appears in an expression
I would like to see how many times (and where) the number "91" appear in a set of formulae.
I thought of using Position[expr , 91 , Infinity], but it seems not to ...
0
votes
2answers
88 views
Learning to work with core pattern only [closed]
I am trying to learn "core" patterns so I can start using them more often. Consider I am trying to solve the following problem.
data = {2,{4,2,3},5,{7,3},{},4,1} (...
2
votes
0answers
29 views
Using Min & Max of an Interval in a replacement [closed]
I want to use a replacement rule to transform a list of equations. The following works as expected:
...
2
votes
1answer
46 views
FreeQ checking for several variables [closed]
I am using FreeQ to define a replacement rule. However, it doesn't seem to be possible to specify a list of variables as the second argument, which is why I came up ...
1
vote
1answer
40 views
Commutativity of Times and pattern matching
I understand that Attributes of Times make a bit non intuitive the Pattern Matching of its arguments.
However I do not understand why this gives False:
...
4
votes
1answer
50 views
String Pattern to match “x by y”
I'm trying to create a string pattern which will match either (with quotes included):
"x by y"
x by y
'x by y'
I've tried to use the following pattern: ...
5
votes
1answer
78 views
Why is { } interpreted as an option in my function? [closed]
I don't understand the output from:
...
3
votes
0answers
83 views
Select certain term containing some patterns and confusing pattern Alternatives in FreeQ
I am considering a function termsContain[func_,list_] which select in an expression func the terms containing the ones in the ...
1
vote
3answers
88 views
Is there a possibility of adding a second condition, or an else clause to $/;$?
Let tally=RandomInteger[{0, 1}, 10];
In the code below, I'm trying to output a list where each component $C_n=\sum^n_{i=1} \text{tally}_i / n$
The problem with my ...
2
votes
1answer
140 views
How to preserve the order of multiplication with Cases?
i have following expression:
Cases[cx[i, k] cx[k, q] a[z, x], _Symbol, 2] // DeleteDuplicates
what i expect is to get:
...
5
votes
2answers
346 views
How to remove the item that is repeated?
If i have a
list={m,n,p,q,q,r,l,l}
how can i remove the repeated item with pattern matching so i would have
...
3
votes
2answers
80 views
Change arguments of a product of functions
I am trying to do the following with rule-based pattern matching
(f1[t] f2[t] f3[t]) /. {x__ -> n[
Product[x[[i, 0]][om[i]], {i, 3}]]} // Quiet
which ...
1
vote
1answer
33 views
Extract powers of exponential into a list
I have a very complicated, long (thousands of terms) expression that boils down to a form of
expr = a1 Exp[b1] + a2 Exp[b2] + a3 Exp[b3]
Note that all a and b ...
5
votes
1answer
139 views
Why Cases and Select treat the List differently?
Look at these two examples:
In[1]:=Select[f[i], MatchQ[_f]]
Out[1]:=f[]
In[2]:=Cases[f[i],_f]
Out[2]:={}
It seems that the Select take $f[i]$ as List, but Cases ...
4
votes
2answers
125 views
Select certain terms in an expression
I would like to have a function to select terms containing q[i] terms in expressions, for example, for an expression
a q[i]+b +c q[j]+d
I would like the function ...
0
votes
1answer
49 views
Replacement of the patterns in the replacement
I want to make such changes:
$(A\, p + B\, q)[i] \to A\, p[i]+B\, q[i]$
But the replacement below can not do this
...
1
vote
0answers
29 views
Remove expression with matched braces from string
I am writing a LaTeX document where the custom command \chg{...} highlights changes in some color. Here I am, with a document of about 50 of those. Sure, one could ...
1
vote
1answer
45 views
Replace an If by a combination using replacement rules
Consider the following code :
tttest = a^2 + If[a > 0, a, -a]
a^2 + If[a > 0, a, -a]
I would like to replace my If function by something like fonction @ ...
