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

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3
votes
2answers
213 views

Finding similar expressions in list

I have a function that returns to me lists of expressions, like: ...
2
votes
1answer
72 views

Matching a list of sequences with common form

I am trying to find a pattern that matches a list of sequences that share a common form. The sequence form is: 1 followed by zero or more nonzero integers, followed by 0. An example list is: ...
1
vote
0answers
80 views

Function behavior based on Head

I'm figuring how to implement a function behavior based on the Head of its argument. I mean ...
3
votes
2answers
690 views

Removing trailing zeros from a list

If I have a list like list1={2334.,342.,0.,0.,2322.,0.,0.,0.,0.,,,,,,}; it's easy to remove to trailing blanks with ...
4
votes
4answers
586 views

More elegant way

I read ReplaceOrRemoveInvalidOrMissingData Mathematica documentation, and I tried to apply the same approach to my dataset. I've got two problems, but one is only a style problem! There is one more ...
3
votes
1answer
191 views

Inheritance in Mathematica using pattern matching on UpValues

Edit: I think in my original post, I missed emphasizing the main point. This is mainly a pattern matching question. If you're interested in the 'why' of this question, please read the original post ...
2
votes
1answer
239 views

Applying rules to rewrite expressions that contain patterns

I'm trying to write a rule that can rewrite a pattern that exists in another expression. For some reason, this is proving to be more challenging than I expected ... most likely because I'm not totally ...
14
votes
3answers
590 views

How to match a cyclically repeating sequence?

I have run across several times recently where I must match a sequence that is cyclically repeating. For example, with the sequence, Sequence[a, b, c] how would ...
0
votes
2answers
243 views

Replace matrix with conditions

I want to replace the values of 1. in slot under the condition that the year and month in basevalue and ...
3
votes
1answer
281 views

Simplify equations with pattern assumptions

When simplifying an expression using Simplify[expr, assumptions], the assumptions has to be explicit. Is it possible to simplify an expression with pattern ...
3
votes
3answers
439 views

How to do Cases with multiple related patterns?

I would like to write a function similar to Cases, but can search for a group of related patterns together. For example, ...
0
votes
0answers
24 views

Manipulating named patterns inside replacement rules [duplicate]

When I evaluate the following expression, {a -> "value1", b -> "value22"} /. {Rule[x_, y_] -> Rule[x, y]} I get ...
1
vote
3answers
115 views
9
votes
1answer
259 views

How to define function that can change patterns

Given time series data as follows: data = {{{2011, 1, 13}, 10}, {{2011, 2, 14}, 17}, {{2011, 3, 15}, 20}, {{2012, 1, 16}, 30}, {{2012, 2, 17}, 40}}; ...
7
votes
3answers
169 views

Checking through an expression

I am writing a code that manipulates expressions that contains functions with an arbitrary number of arguments. An example expression is ...
3
votes
1answer
149 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 ...
3
votes
1answer
99 views

Elegant way to match a list with only certain types of elements

I'm working on learning Mathematica programming for personal edification and am trying to find a more elegant way to do a matching expression which will match only a list containing elements that are ...
3
votes
2answers
251 views

Extracting argument sequences from function expressions

Why is it that fun[x, y] /. fun[z__] :> z leads to Sequence[x,y] but ...
3
votes
2answers
213 views

truncating terms in symbolic expression basing on their values

I need to simplify big symbolic solution of equations system by truncating terms that are orders of magnitude less then others in subexpressions like a + b. The solution is big fraction with sum of ...
0
votes
2answers
212 views

Pattern matching

This is a very simple question I hope you can help me with. I am experimenting with pattern matching. I want to write a pattern for a difference between two symbols, ...
4
votes
1answer
90 views

Dot when used in a pattern becomes Times… Why?

In[1] := Hold[a.b] // FullForm Out[1] := Hold[Dot[a,b]] So far so good. ...
5
votes
2answers
453 views

How to test whether an expression is a valid variable?

I would like to test whether an argument is a valid variable for functions like Solve and DSolve. For instance several ...
9
votes
2answers
285 views

Using Except with strings

Suppose that I have the following sample list, called list: list = {"bBb", "aAa", "aaa"}; Now suppose I want to select the ...
4
votes
1answer
141 views

Selecting expressions from a sequence that are not subexpressions of earlier elements

I have a While loop that generates and prints an expression on each iteration (there can be thousands of iterations). UPDATE: Some expressions are generated in ...
4
votes
2answers
97 views

Pattern-rewriting Pattern triggers error?

I am trying to rewrite patterns. For example, I'd like to rewrite the pattern jFoo_Integer which has FullForm ...
9
votes
2answers
261 views

Orderless pattern matching of rule lists

I am looking for a compact way to specify a pattern to match a rule list with MatchQ that allows for enumerating the rules in the rule list in an arbitrary order. ...
12
votes
4answers
432 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): ...
3
votes
2answers
213 views

String pattern matching & replacement

I would like to find all occurrences of a full stop "." followed by a capital letter in a string and have these replaced with a "; ". How do I do this in Mathematica? e.g. ...
17
votes
1answer
259 views

Bug in RepeatedNull?

RepeatedNull appears to be buggy (versions 8.0, and 9.0). Define f as follows: ...
4
votes
5answers
339 views

Pattern matching in nested lists

I'm sure this has been asked before, but I can't find the right combination of search keywords to find it. Apologies. I want to do a ReplaceAll on a list of lists, ...
4
votes
0answers
243 views

Syntax error for optional pattern, but only in debugger

This expression (explained here by Leonid) evaluates fine unless Evaluation->Debugger is enabled: h[x : (_Integer) : 1] := x Syntax::sntxf: "x:" cannot be ...
6
votes
4answers
321 views

Is there a more Mathematica-y way to label these plots?

I am studying an infinite square well in the context of quantum mechanics. ...
2
votes
1answer
121 views

Function to differentiate between date pattern and specific string format

I'd like to write a function that behaves one way when the argument is a Mathematica date, such as {2013,12,15}, or with added hours, minutes and seconds if ...
2
votes
1answer
230 views

How to create a SparseArray satisfying multiple conditions on Parts and Elements of a Matrix?

I have a matrix m1 of size $3 \times 19$. Rows $1$, $2$ and $3$ represent $3$ different groups, and columns represent $4$ different blocks: block1 - columns $1$, ...
1
vote
0answers
43 views

Matching Root[…] objects with patterns, unexpected hidden argument

I needed to write patterns that could distinguish between arbitrary-function and polynomial forms of Root objects, for example, ...
1
vote
1answer
656 views

How to effectively compare two sentences and say both are equal

want to compare two text file. Suppose file AA contains following text ...
1
vote
0answers
37 views

Pattern matching list elements in pure functions [duplicate]

Pattern matching here is a functional programming term, but it might be called differently in Mathematica, I'm not sure. It is possible to match the elements of the list in a regular function ...
6
votes
3answers
213 views

Using PatternTest and/or Condition to detect equal list lengths as well as list element formats

On searching Mathematica.SE for information about overloading functions, I came across several threads about PatternTest and ...
4
votes
3answers
214 views

Simplifying expression with patterns (Replace)

Q1: I need to simplify some algebraic expression, according to particular pattern, namely: \begin{equation*} x^m = \left\{ \begin{array}{ll} 1 & \text{if } m \text{ is even} \\ x & \text{if ...
1
vote
1answer
91 views

Substitute complex functions into complicated polynomials

Mathematica has some strange way of sorting terms. It seems that it is using a canonical sort on expressions, e.g. $\mathbb{i} \sin[x] \cos[y] \cos[z]$ is returned as $\mathbb{i} \cos[y] \cos[z] ...
3
votes
1answer
290 views

Extract date from a not well-formed string

Is there a way to robustly extract date and time from a text? Say for example: ...The event will be held on 17/10/2013 at 3:30 PM in the room 121 and everyone is welcome... should return: ...
12
votes
10answers
725 views

Counting sublists containing 0

Given a list: data = {{0, 2}, {0, 0}, {1, 0}, {1, 2}, {2, 3}}. I would like to count the number of sublists which contain zero. ...
5
votes
1answer
374 views

Use Pattern with Vectors in Assumptions

I had a problem using Pattern with Vectors in Assumptions. Here's how I use ...
2
votes
1answer
178 views

Elegant transformation of various rules to strings, {f[z_] -> y} becomes “f = @(z) y”

Assume that I have some function for transformation mathematica expressions to strings. For simplicity, just assume it is an identity: ...
3
votes
1answer
242 views

Is there a way to simplify this replacement rule

I have a rather big expression which contains many sums of form q x + w y. I know that y is much smaller than ...
14
votes
2answers
351 views

Pattern to match L, but not L[_]

I have an expression where I want to replace L but not L[_] For example, the following doesn't work and ...
13
votes
5answers
664 views

How to remove duplicate characters from a string?

How do you remove duplicate characters in a string without converting the string to a list. I want to delete all duplicate characters in a string (i.e. get the unsorted union of characters). For ...
9
votes
1answer
124 views

Why can't I remove the {0, 0} in Circle[{0, 0}] using pattern matching?

Why does Circle[{0, 0}] /. List[_?NumericQ ..] :> Sequence[] return Circle[{0, 0}] yet ...
2
votes
3answers
393 views

How to manipulate log arguments?

A common problem I have with Mathematica is needing to manipulate the arguments of logarithms. Typically, I need to take ratios of the log arguments Mathematica gives me by default. That's to say ...
2
votes
0answers
400 views

NDSolve Issue with initial conditions

I am trying to implement a Poincare section for a gravitational movement on the plane $(x,y)$. Here is the code I wrote ...