Questions on expression testing and manipulation through pattern matching and constructing efficient patterns.

learn more… | top users | synonyms (1)

3
votes
2answers
57 views

Why does `Repeated` not work in this case?

I think I don't understand how to use Repeated. I have a list for example list={a,b,a,b,a,b,a,a,b} I want to detect whether ...
6
votes
2answers
99 views
3
votes
1answer
149 views

Is this a bug in NCAlgebra library?

In course of my work with NCAlgebra package for Mathematica, http://math.ucsd.edu/~ncalg/ , I encountered unexpected behavior of replacements. I am using ...
4
votes
1answer
127 views

How can one match a function in a replacement rule

I'm trying to write a delayed replacement rule that is capable of matching both the functions and their parameters, like ...
26
votes
5answers
2k views

Fetching data from HTML source

I want to generate a couple of plots/graphs with Area 51 statistics. Since Area 51 doesn't work with the SE API, I'm forced to find another way to get the information I want. That other way is with ...
16
votes
4answers
479 views

How to enumerate all possible binary associations?

Suppose I have a list of symbols like: {a,b,c,d} I would like to enumerate all possible binary associations (combining symbols and/or sublists pairwise): ...
8
votes
1answer
119 views

What kind of pattern should I use with StringCases?

Consider the string str = "ABCaDEFbcABCdefDEF" I'd like to take out all substrings surrounded by the substrings "ABC" and ...
2
votes
1answer
53 views

Why is head evaluation inconsistent in pattern replacement?

I noticed the following unexpected result: In[90]:= "foo" /. x_String -> Head[x] Out[90]= Symbol Why is it that Head[x] ...
12
votes
1answer
206 views

Longest common substring for multiple strings?

I'm looking for a way to get the longest common substring for multiple strings such as {home/dir1/dir2/jmoasd.txt,home/dir1/dir2/ivbnoxcihv.txt,home/dir1/dir2/siuhgiuchv.txt} should yield ...
4
votes
3answers
54 views

pattern matching for third degree reciprocal equation

I am trying to create a pattern for third degree reciprocal equation. I try this a_ + b_ x_ + b_ x_^2 + a_ x^3 This matches ...
4
votes
0answers
37 views

Pattern match Shortest BlankNullSequence in SequencePosition

Apologies if this has an answer somewhere but I can't find it. From the examples for SequencePosition we are shown that ...
1
vote
2answers
107 views

Filtering and summing sublists with Cases

I've declared a list: list = {{1, 2}, {2}, {3, 4, 1}, {5, 4}, {3, 3}, {a, b, c}, {e, f}, {g}, {}, {Sin[a], Cos[b]}}; now I've made an rule which add 2 pairs ...
5
votes
0answers
120 views

Same input,different result? [duplicate]

Using this code,you can see,same input, but the output are different. So weird! If I copy this code here, it outputs normally. So what's the problem? Ps:I use ...
0
votes
1answer
62 views

Pattern which will transform a given expression [closed]

Find the Pattern which when applied to this expression expr = {a^2, a^b, x^4, (x - 1)^2}; yields this result: ...
1
vote
0answers
40 views

Rule/Replace/Patterns [closed]

I need help with doing this question. given: Sin[x+y] Cos[x+y+z] Define using Patterns a rule (specifically a list of 2 rules ) , the two adding rules for trigonometric functions sin (a + b ...
4
votes
1answer
56 views

How to check if an expression contains a symbol ONLY after a given head?

I have just started programming in Mathematica and still have to get a hang of it (and rule-based programming), so I apologize if this question may seem stupid. I will explain it with a concrete ...
10
votes
2answers
115 views

Using Cases to pick out entries of a SparseArray

I'm trying to use a SparseArray for some large homological algebra calculations. I'd like to find indices of a SparseArray ...
3
votes
1answer
75 views

Replace pattern for exponentials

Ultimately, I want to replace every Exp[(const) w[i,j]] to T[i,j] and Exp[-(const) w[i,j]] to 1/T[i,j] in the following expression ...
21
votes
7answers
1k views

Using patterns in pure functions

Pure functions may be handy if you don't want to assign your function a name. For example I would calculate $x(x-1)$ for some numbers $x$ by ...
2
votes
2answers
63 views

How to make a replacement, provided an inner rule applies

Consider: expr /. (b[a_] * c_f /; !FreeQ[c, d[a]] :> (c /. (d[a] :> e) )) Here's how it works: in expr, the products ...
1
vote
0answers
80 views

How to “INJECT” with holding Evaluation, specifically into a WhenEvent

I am importing a set of differential and stochastic equations from an external package, and want to use Mathematica to analyse this. I am struggling building the set of equations that I can use with ...
10
votes
2answers
83 views

How to use `Except[]` inside of `Pick[]` [duplicate]

Pick[{1, 2}, {0, 1}, Except[0]] returns {1, 2}, the first element of which I did expect to be excluded. What is the thing I ...
7
votes
1answer
77 views

How to match Association[]?

The following input: Cases[{"key" -> Association[]}, HoldPattern["key" -> Association[]]] Returns {}. Why does it not ...
2
votes
0answers
41 views

Replacement rule for summation with Kronecker delta

I want to perform some symbolic computations in index notation, without explicit reference to sums, so that in expressions of the type f[i,j]g[j,k] summation over ...
8
votes
1answer
86 views

Matching HoldPattern expressions

My original problem is to delete all rules starts with a[1] from SubValues[a] For example, ...
4
votes
2answers
206 views

Pattern Matching for Rules [duplicate]

Consider a set of rules, e.g. {a -> aa, b -> bb, c -> cc, d -> dd, e -> ee} I want to remove from this list all patterns of the form e->_ and to ...
0
votes
0answers
12 views

How to match sum of two or more objects? [duplicate]

I am trying to match expressions that are the sum of two or more objects with a specific head. However I can not get this work properly. For example ...
19
votes
2answers
320 views
4
votes
2answers
79 views

MatchQ failing in some cases with Hold [duplicate]

Could someone clarify why the first of these MatchQ finds a match whereas the second does not? (I'm using version 10.0, in case that matters.) ...
1
vote
1answer
41 views
6
votes
1answer
102 views

StringPattern to remove markers around text

I am not able to figure the StringPattern to use to remove markers in string. This is the input. ...
11
votes
0answers
108 views

Logical AND of multiple patterns

Mathematica provides an equivalent for "logical OR" when pattern matching, using Alternatives or the infix | operator. For ...
1
vote
0answers
79 views

Matching All Functions [duplicate]

Is there any way to match all functions? There's an existing answer for matching functions of one parameter (_@_) but it doesn't work for trying to test if a symbol ...
0
votes
2answers
86 views

List of all Variables that match an specific pattern

I'd like to make a list of all constants that match an specific pattern, wich includes all terms that multiply an specific variable. For example, I'd like to take all terms that multiply t in: ...
11
votes
2answers
303 views

How can one represent a string pattern with prohibited substrings?

Say I have the following string: "<hello>something WRONG</hello><hello>something else</hello>" I am trying to find code that works like the ...
9
votes
2answers
211 views

Test for non-numeric variables

I have a table, testdata, with numeric and non-numeric data. testData = {{1, 2, 3, no, 5}, {5, 6, 7, 8, 9.1}, {1, y, y, n, n}}; I can locate the positions of ...
3
votes
1answer
126 views

Specifying string patterns in a plain text

I need to extract three data, like that: (1.05, 1.37,A) from an imported list of plain texts: "... Syntax of parallax is : 'value quality [error] bibcode' value : parallax value quality : flag ...
5
votes
1answer
67 views

Matching products with optional factors with definite heads

I need to match a products with exactly one factor F, an arbitrary number of factors of head A, and possibly additional inert ...
4
votes
1answer
27 views

How to get the VertexWeight list or EdgeCapacity list in a graph

The graph of Mathematica.We have VertexList or EdgeList.So we can get it convenient like ...
4
votes
1answer
220 views

How to Override the Head of a Symbol

I was wondering if it is possible to override the head of symbols/operators. As a motivating example if I run: Then Ket will be returned. But lets say I want Bob to be returned instead of Ket. Is ...
5
votes
1answer
66 views
4
votes
0answers
53 views

How to get f[x] to match with f[c_., x] when OneIdentity doesn't match

After setting: SetAttributes[f, OneIdentity] Default[f] = 1; We have the following successful matches: ...
2
votes
4answers
141 views

Finding the maximum order derivative of an expression

I have an expression that is the the sum and product of undefined derivatives and their derivatives. e.g. fg+ Dt[f,t]g +Dt[g,{t,2}]f+ What I would like to find ...
0
votes
2answers
59 views

replace a part of equation by a symbol

I have an equation: $$ \frac{d\text{$\phi $0}}{dx} \left(-\frac{\text{A1}(x) \frac{d\text{A0}}{dx}}{\text{A0}(x)^2}+\frac{\frac{d\text{A1}}{dx}}{\text{A0}(x)}+\frac{\text{B1}(x) ...
8
votes
2answers
194 views

Odd behavior in pattern matching for functional form

Consider the two seemingly closely related operations: ...
45
votes
2answers
1k views

How is pattern specificity decided?

Mathematica has a notion of pattern specificity, which is a partial ordering on patterns. The rules (e.g. DownValues, ...
3
votes
2answers
50 views

Strange behavior with Inequality and pattern matching

An expression like this one a < x < b is normally represented as Less[a, x, b] while an expression like ...
0
votes
1answer
59 views

Extracting attributes from a function [duplicate]

From an expression describing a mathematical function, I would like to extract its parameters. For example, from the expression 4 Sin[2 a x^2 + b x + c], assuming ...