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

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6
votes
5answers
235 views

Extracting sequences from a list?

Suppose I have a list of arbitrary length like {1, 2, 3, "Open", 3, 2, "Close", 9, 3, 4, "Open", 1, 0, "Close", 3, 5} and I am trying to extract the sequences ...
6
votes
3answers
138 views

Pattern matching: Times[a_] vs Times[a__]

I don't understand why MatchQ[ HoldComplete[Times[3, 2, 2]], HoldComplete[Times[a_]] ] is returning True. I thought that ...
6
votes
2answers
235 views

Apply Trig Identity to Transform Sum of Sinusoids into Phase-Shifted Cosine Function

I'm trying to solve for the output of a simple RC low-pass filter, with Cos[w t] input. The convolution of the input with the RC transfer function gives me the right output, but I'd like to be able to ...
6
votes
3answers
189 views

Strange behavior of MemberQ, Position

After importing an array of latitudes and longitudes and trying to find the position of some latitudes I was encountered with an unexpected problem since certain values could not be found for some ...
6
votes
2answers
266 views

Formatting text through pattern matching

I am trying to format some text based on some patterns. ...
6
votes
1answer
244 views

Match sequence of zero or more characters except a given character

This looks like it should be simple: I want to match an "i" followed by an "o" with an arbitrary (possibly zero-length) sequence of characters in between, unless that sequence also contains an "i". ...
6
votes
1answer
490 views

Count sublists which match pattern

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which: have both slots zero the ...
6
votes
2answers
237 views

Variable scoping problem when mapping over delayed replacement

This is something that got me curious while I was playing around with Mathematica. Consider the following (contrived) example: ...
6
votes
1answer
254 views

How to set up new types for pattern matching strings?

Consider the following toy example: I have a set of language sounds, which I partition into two exclusive subsets, consonants and vowels. I want to set up string patterns for e.g. ...
6
votes
1answer
323 views

Pattern matching in subscripted variables

I am trying to use subscripted variables as symbols and provide assumptions elegantly for them, e.g. in order to simplify logs, I'd like to have ...
6
votes
1answer
246 views

Pattern definition for replacing plus and subtract

Suppose I have two functions $h_1(x)$ and $h_2(x)$, for which we know their sum and their difference: $$ h_1(x)+h_2(x) = d(x) \qquad h_1(x)-h_2(x) = i f(x) $$ I have a complicated expression, in ...
5
votes
4answers
798 views

Creating lists from a string, separating words from numbers

Say I have a string that contains numbers and words, such as this one: string = "there are 1234 words and numbers 5678 in here $999"; How would I separate the ...
5
votes
3answers
481 views

Camel hump string split

Given System names of 2 or more characters: systemNames = Names["System`*"] // Select[StringLength[#] > 1 &] ; Is ...
5
votes
5answers
582 views

How can I use nested conditionals inside my functions?

I'm a big fan of using conditionals inside my functions to deal with cases, that is, to pattern match in stages and possibly leave a function unevaluated. ...
5
votes
3answers
633 views

position of sequence of elements in list [duplicate]

Possible Duplicate: Finding a subsequence in a list Question The position of {3, 5} is the list {1, 3, 4, 3, 5, 5, 1} is 3. How can such a position ...
5
votes
5answers
193 views

Counting subsequences (i.e., patterns) within a list?

I would like to count the number of subsequences in list. Say I have data given by: data = {1, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1}; I would like to count the number ...
5
votes
2answers
203 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 ...
5
votes
5answers
141 views

Isolating cross terms

I have a set of expressions that contains terms like $\frac{1}{(x + a + b)(c+d)}$. I would like to simplify the denominator so that products of $a,b,c,d$ are dropped, but $x c$ and $x d$ are kept. ...
5
votes
4answers
269 views

Pattern matching - comparing two lists

I would like to compare two different lists to see if the shorter one is a member of the larger e.g. is the list {2,3}, with that sequence of elements, a member of {1,2,3,4,5}? I have tried using ...
5
votes
3answers
218 views

Converting expressions to “edges” for use in TreePlot, Graph

This question is similar to this: Nested list to graph. How to "flatten" an arbitrary expression, eg expr = a[b[c, d[e][f], g], h] to a list of key-value pairs ...
5
votes
2answers
234 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 ...
5
votes
4answers
108 views

String matching balanced pairs of braces

I am trying to extract from a string in Mathematica all instances of \newcommand{ABC}{DEF} Where ABC and ...
5
votes
4answers
175 views

Finding the position of a single array in a list of arrays that contains wildcard variables

Consider two lists: superList = {{wc,wc,1,wc,wc}, {wc, wc,2, wc, wc}, {wc, wc, 3, wc, wc}, {wc, wc, 4, wc, wc}}; littleList = {a,b,3,c,25}; In ...
5
votes
3answers
159 views

Pattern match for nested Association

Suppose I have Association testAssoc=Association[a->Association[1->1,2->2],b->Association[1->1,2->2]] which ...
5
votes
1answer
212 views

Sentiment analysis of tweets

I want to use Mathematica for a sentiment analysis on tweet-messages. For that purpose i selected several tweets. Each tweet is interpreted by myself as positive (pos) of negative (neg). For example: ...
5
votes
2answers
352 views

Keep Ordering of Bra Ket When Printing

I would like to keep the ordering of the bra ket-print but right now this doesn't happen. Any Idea? I tried playing with HoldForm but then i could evaluate the expression inside properly ...
5
votes
3answers
378 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 ...
5
votes
2answers
229 views

Pattern matching deletion of list items [duplicate]

Possible Duplicate: How can I remove B -> A from a list if A -> B is in the list? I'm working toward building a graph and use some code to construct my rules which results in a form ...
5
votes
2answers
206 views

Delete contexts from a string representation of a symbol

I want to delete the string representing the context of a symbol. For info I need such a functionality in my ShowIt function defined here I'd like to know how I ...
5
votes
2answers
122 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
1answer
279 views

Why does this pattern for combining two lists require triple underscores (___) to work?

I understand that __ is a list of one or more elements, and that ___ is 0 or more elements, but when I try this rule with 2 ...
5
votes
2answers
208 views

Why rule does not work if Flat attribute?

The following works: ...
5
votes
1answer
230 views

More efficient Omnibus number determination?

Amusing myself with concepts from "Omnibus Sequences, Coupon Collection, and Missing Word Counts", in particular the sequences. To paraphrase the concept, a string is k-Omni over some alphabet a if ...
5
votes
1answer
340 views

Use Pattern with Vectors in Assumptions

I had a problem using Pattern with Vectors in Assumptions. Here's how I use ...
5
votes
0answers
239 views

Convert logical relational expression to / from disjunctive and conjunctive forms?

I would like to convert logical relational expressions in disjunctive form, e.g., $$(x \lt -1) \lor (-1 \lt x \lt +1) \lor (x \gt +1)$$ into conjunctive form, e.g., $$(x \ne -1) \land (x \ne +1)$$ ...
4
votes
2answers
866 views

Classifying poker hands by pattern matching

I am working on this question posed in a Mathematica course revised in 1998. Here are the instructions: Poker Hands You are to define and show working examples of a function "...
4
votes
7answers
428 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 ...
4
votes
2answers
310 views

Why can't NumberQ be used as the head of a pattern?

Consider the following: list={1/First[{}], 1, 2, 1/First[{}], 3}; DeleteCases[list,_NumberQ] I wanted to remove all cases, which did not match ...
4
votes
6answers
2k views

Removing zero values from ordered pairs

I have some processed data, which are basically a collection of ordered pairs in the form: {{x1, y1}, {x2, y2}, ..., {xn, yn}} Ordered pairs which have either a ...
4
votes
5answers
529 views

How can I name patterns in a Switch expression?

Suppose I have an expression and want to match it against successive patterns and return an expression corresponding to the first pattern that matched. In that case, I can use ...
4
votes
2answers
119 views

Pattern matching not going over a list when using default values

if I execute the following command in Mathematica: {a,a^2,a^3}/.a^(n_:1)->b^(2 n) Mathematica returns: {b^2,b^4,b^6} ...
4
votes
5answers
290 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
2answers
175 views

How to use Optional as an omissible parameter in pattern-match?

Below is a function intended to test if an expression is a polynomial in which all the coefficients and exponents are integers: ...
4
votes
4answers
154 views

Cases with Alternatives failed

Consider this list of rules rules = {a -> 1, b -> 2, c -> 3} I'd like to fish some of the rules out of such a list using ...
4
votes
6answers
445 views

Command to take the first elements of a list that match a pattern

I want to find the number of elements in a list in a row that match a certain pattern. So for this list {1,1,1,1,0,0,0,1,1,1} It should return "4" because there ...
4
votes
3answers
471 views

Function with zero or one arguments

Is there a neat way to define a function with a single optional argument that defaults to an empty sequence? For example, suppose I want to define a wrapper for ...
4
votes
3answers
195 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 ...
4
votes
2answers
259 views

Pattern matching repeated structures with named subexpression components

I am trying to write a function with a pattern that tests its arguments for a particular structure. But in that pattern I'd like to name a subpattern to make it easier to exract and operate on. The ...
4
votes
1answer
112 views

How can I extract all the non-number symbols from an expression [duplicate]

If I have an expression, let us say something like this: Cos[3 x] + π/cofe Exp[y^(c z)] how can I get all non-number symbols in the expression which are: ...