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

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6
votes
2answers
127 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
2answers
70 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 ...
8
votes
2answers
182 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
339 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): ...
16
votes
1answer
236 views

Bug in RepeatedNull?

RepeatedNull appears to be buggy (versions 8.0, and 9.0). Define f as follows: ...
3
votes
2answers
144 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. ...
3
votes
4answers
188 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, ...
6
votes
4answers
275 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. ...
4
votes
0answers
116 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 ...
2
votes
1answer
109 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
156 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
36 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
186 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
32 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
163 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 ...
3
votes
1answer
184 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: ...
4
votes
3answers
141 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
65 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] ...
5
votes
1answer
236 views

Use Pattern with Vectors in Assumptions

I had a problem using Pattern with Vectors in Assumptions. Here's how I use ...
13
votes
6answers
2k views

Counting negative values in list

I would like to count the negative values of a list. My approach was Count[data, -_] which doesn't work. How can I tell Mathematica to count all numbers with ...
12
votes
5answers
488 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 ...
2
votes
1answer
149 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
147 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 ...
13
votes
2answers
308 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 ...
9
votes
1answer
109 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
153 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 ...
5
votes
2answers
198 views

How to get complement of a pattern

I have a list. I want to get all the elements in that list which do not match a given pattern. That is, I want the strings which do not match any of the following patterns: First and last characters ...
2
votes
0answers
180 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 ...
3
votes
1answer
90 views

Use of StringExpression as argument

Is it possible to use a StringExpression as a pattern for an argument? I.E. something like foo[chars__~~ WordCharacter.. ~~ num:NumberString] := {chars, num}; At ...
1
vote
1answer
164 views

Do any users know of methods to capture Twitter feeds and subject them to analysis? [duplicate]

I would like to use the output of about 300 Twitter sources and would probably collect 30 minutes of tweets at a time and subject each collection to analysis; ideally this process would be automatic ...
17
votes
1answer
183 views

How to get Cases to wrap results in an arbitrary head?

A number of functions provide for results to be wrapped in an arbitrary head. This is very important in cases where the results should not be evaluated. Take ...
2
votes
3answers
301 views

Select sublists with second element nearest to zero

I've got some big lists from which i need some data (one of the big lists). To be specific, I need to divide this biglists in sublists of the same length (10000), and form a new list with the mean of ...
5
votes
2answers
107 views

Pattern Matching with Indexed Object

If I have a list of rules associated with indexed variables like: solution = {a[1] -> 1, a[2] -> 10, a[3] -> 100} I would like to be able to extract all ...
5
votes
3answers
288 views

Highlighting text with StringReplacePart but also using Style, Subscript

For a Natural Language Processing analysis task it's desirable to highlight a text string programmatically according to XML tags that reference specific words or phrases. The XML tags specify the ...
8
votes
3answers
191 views

Select and Blank

I try to filter sublists of a list which match a pattern. test = {{"String1", "a"}, {"String2", "b"}, {"String3", "a"}, {"String4", "a"}}; The result should ...
4
votes
7answers
361 views

Given a symbolic expression how to find if starts with a minus or not?

I am using a Mathematica function which returns some error term in symbolic form. I needed a way to determine if this term starts with a minus sign or not. There will be only one term This is to ...
20
votes
1answer
612 views

replacement rules from a pattern and a matching expression

(This seems to be a very basic necessity in a language having pattern-matching capabilities such as Mathematica, yet I struggled for many hours to find a common solution to this problem.) Suppose ...
2
votes
1answer
153 views

Add Pattern to List Removing Duplicates

Lets say I have a list of patterns ...
7
votes
2answers
198 views

Using MatchQ (or other means) to parse an expression using sums of COS or SIN correctly

I am writing a function that will take an expression as input. I want to make sure the expression is valid first before processing it. Looking for a correct to use ...
2
votes
1answer
125 views

Match a sequence of integers

I would to match a pattern p1 = 0,0,1,0,0 to the elements in listA. The elements are a boolean sequence that may look like this ...
10
votes
3answers
169 views

Pattern matching on Orderless functions inside Hold

MatchQ[Hold[1 + 2], Hold[2 + 1]] returns False. But in the presence of a Blank[] in the ...
4
votes
4answers
341 views

Listing matrices up to symmetry

I am interested in the equivalence relation on N x N binary matrices, in which two matrices are equivalent if one can be obtained by rotating/reflecting the other. I would like to obtain a list ...
1
vote
2answers
179 views

Collect pattern (Log's)

Is it possible to apply "Collect" command (to put Log's in particular combination) to factor out (pattern) a particular form from the full expression. For example, consider the following expression: ...
2
votes
0answers
31 views

Detecting a more general pattern [duplicate]

I need a function that, given 2 patterns, determines if the first pattern is more general than the second (i.e. that any expression successfully matched by the second, will be successfully matched by ...
2
votes
3answers
225 views

Isolating a prefactor in an analytical expression

I have a large mathematica expression that looks roughly like f = A1 Exp[a1 x] + A2 Exp[a2 x] + b1/x + b2/x^2 + c0 + c1 x + c2 x^2 where all the ...
9
votes
1answer
101 views

Apply N only outside a certain function

1 + f[1] // N gives 1. + f[1.] I don't want the argument of f evaluated by N; I ...
19
votes
7answers
974 views

Elegant and fast way to join all string sequences

I want to do what title says: {"a","b",1,2,3,4,"a",2,2,2,"edg","?"} => {"ab",1,2,3,4,"a",2,2,2,"edg?"} in the most elegant way. For example one replacement rule for ...
1
vote
1answer
93 views

How to define Similarity Rules?

I have a question about Mathematica's SimilarityRules defining (for e.g. SequenceAlignment function). So help centre clearly ...
10
votes
4answers
224 views

Is it possible to separately call the default value of a variable which isn't at the end of the sequence?

After reading this post I recalled an old question I once met. We know that we can set default values for variables of a function: ...
5
votes
2answers
168 views

Extract substring by repeated StringPattern

This code failed, but may exemplify my intention. StringCases["aA1bbbbbbbbbbaA2baA3b...aA4b",Repeated[Shortest["a"~~xx__~~"b"],{2,100}]] I want to get the ...