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

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5
votes
3answers
171 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 ...
1
vote
2answers
98 views

text analysis: split document in seperated lines

For a text analysis I want to split a large document in seperated lines. Then I want to calculated for example the average number of words. A example of the document is the following: ...
5
votes
4answers
283 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
1answer
239 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: ...
3
votes
2answers
156 views

Convert matrix rows into variables

Can anyone show me how to set all matrix rows to variables. For example, I have matrix w={{1,2,3},{3,2,1},{0,0,0}} and I need to set each matrix row to be separate ...
13
votes
1answer
104 views

Report: IgnoringInactive: a bug?

Bug introduced in 10.0.0 and fixed in 10.0.1 Just to report. IgnoringInactiveshould work with Cases. In agreement with the ...
1
vote
1answer
94 views

Function returned an unexpected list

I was trying out a question in Wellin's Programming with Mathematica that says the following. Question: Given a set of points in the plane (or 3-space), find the maximum distance between any pair of ...
1
vote
0answers
47 views

How to pattern match an association? [duplicate]

I have the following: Clear[a, b]; a = {{1, 2, 3}, {4, 2, 5}, {6, 7, 8}}; b = GroupBy[a, #[[2]] &]; b whose output is: ...
11
votes
4answers
282 views

Recognizing special cases of a defined function for permuted arguments

I have a number of ugly ways to implement the following pattern recognition task, but I'm looking for something elegant to keep my notebook tidy. I need to define a function of six variables ...
7
votes
5answers
423 views

Splitting strings at lower case characters and numbers

I'm trying to split the strings of chemicals into their elements and numbers. See this example "Fe3O4" will be split into ...
6
votes
5answers
434 views

The correct pattern for Cases

I have a problem that, admittedly, I have already solved using Select instead, but it is irking me that I cannot seem to construct the right pattern to solve it ...
0
votes
0answers
56 views

On the order of rules specification [duplicate]

I wanted to understand how Mathematica parses function definitions in rules-based programming, so I started with the simple code: ...
7
votes
5answers
425 views
10
votes
4answers
404 views

What is the correct way to use specific rule for specific pattern match when parsing an expression?

update: Thanks for the answers below. But I noticed they do not handle the following special cases: lis=1 and lis=z , ...
0
votes
0answers
71 views

Making a list of terms ordered by product order

I have some expressions f,g,h that are elements of a symmetric tensor algebra. The expressions are generated by a basis ...
1
vote
3answers
80 views

Store matched variables

Edit: I am matching and replacing a particular expression. At the same time... I want to store matched variables for later use. I got it to work with messed up code involving ...
4
votes
1answer
127 views

What would be a pattern for a general row of an identity matrix?

I know this is a novice question but I would like a pattern for a list containing zero or more zeros followed by exactly one 1, followed by zero or more zeros. Something like: {0___,1,0___} But ...
2
votes
3answers
113 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 ...
17
votes
2answers
408 views

Pattern that matches colors

Suppose I'm writing a function that takes a color as a parameter; for example: drawShape[color_] := Graphics[{Style[Disk[], color]}]; But if the caller inputs an ...
6
votes
3answers
215 views

Problem with WordBoundary in string patterns

I am trying to extract from a string all words that end with "-man", but the problem is that WordBoundary does not seem to work as it returns whole string ignoring ...
1
vote
2answers
69 views

How do I format expressions so that replacement rules correctly apply to exponents? [duplicate]

I have a series of rules that I would like to apply to a series of expressions with variables, but cannot get Mathematica to correctly recognize that these rules should apply when my variables have ...
1
vote
4answers
179 views

Need an efficient way to do this list manipulation

Lets say i have two lists with me as given below: l1 = {4, 6, 8, 9, 10, 12}; l2 = {2, 3, 4, 5, 6, 7}; Now i have a function S2P(details irrelevant) which takes ...
3
votes
2answers
325 views

Using ReplaceAll to replace a head

Why would this work to replace the head b with newHead: ...
8
votes
1answer
128 views

How to get a list of all expressions in a notebook matching a certain pattern?

Suppose I have a Mathematica notebook saved to a certain location on disk. Given a pattern I need to get the list of all expressions matching this pattern that appear in input, output or print cells ...
0
votes
0answers
42 views

How to correctly use PatternTest (?) [duplicate]

This works fine: {3, -5, 2, 7, -6, 3} /. x_ /; x < 0 :> 0 (*{3, 0, 2, 7, 0, 3}*) and this works fine: ...
0
votes
1answer
48 views

Replace all instances of Integrate by NIntegrate and add a Method option

I have an analytic expression which involves several integrals Integrate[f[x], {x, lb, ub}] where the functions f and bounds ...
3
votes
1answer
341 views

Covariant derivative for symbolic tensors

I want to define a "prefix" (D_i) covariant derivative operator CD[] for symbolic tensors in form of a function, i.e. for ...
14
votes
1answer
381 views

MatchQ-ing Associations (MMA 10)

Consider {x->1} which has FullForm List[Rule[x, 1]] and, therefore, ...
2
votes
1answer
92 views

How to efficiently process pasted content from PDF

I had selected a matrix in a PDF file, and paste it onto my MMA notebook. Below is the exact copy-pasted content: ...
0
votes
0answers
29 views

Problem with replacing a head with another head using pattern [duplicate]

Why would this work Times[a, b, c, d] /. Times :> List (* {a, b, c, d} *) but this doesn't work (the Times still remains ...
3
votes
1answer
58 views

Need help in building a pattern [duplicate]

Suppose I have the following list: list = {w, r, {f, first, t, y}, {a, y}, last, {k, r, first, e}, m, e, last, r, t} I am expecting this ...
12
votes
1answer
205 views

Why doesn't repeated PatternSequence work with explicit pattern names?

Why would this work: Clear[f] f[a : PatternSequence[b_, c_]] := {a}; f[1, 2] (* {1, 2} *) and this also works: ...
6
votes
3answers
190 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 ...
-1
votes
3answers
104 views

How do i import a list of files, choosing the name

I have this list of files, i'm using FileNames[{"*.txt"}, NotebookDirectory[]] to import it, but i just want the ones without inelastic on the name. How can i select just by the name? Thanks ...
4
votes
2answers
138 views

Get part of lousy data

I want to get part of large data. some part of this data is as follows: ...
3
votes
1answer
131 views

Why does pattern test not work in this case to restrict the function parameters?

I was looking at this Q&A about using pattern test (pattern_?test) vs pattern condition (pattern_/;cond) and came across ...
0
votes
1answer
77 views

How can I represent this automorphism of Q(i,a)?

Let $a$ represent some real irrational number. I am trying to perform computations with an automorphism $f:\mathbb{Q}(i,a)\to\mathbb{Q}(i,a)$ which fixes $\mathbb{Q}(i)$ pointwise and maps $a$ to $i ...
5
votes
3answers
485 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 ...
3
votes
2answers
161 views

What is the correct way to pattern match nested lists?

I have the following function: f[lst_List /; MatchQ[lst, SOME PATTERN HERE]] := ({#[[1]] + #[[2]], #[[1]] - #[[2]]} &) /@ lst; I want to match lists that ...
4
votes
2answers
373 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 ...
1
vote
2answers
81 views

Pattern matching to head with HoldFirst

I want to define a function that only operates on expressions with a head from a given list, such as f[expr:(_And|_Or)] := Print["LHS is ", expr[[1]]]; This of ...
5
votes
1answer
233 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 ...
6
votes
3answers
229 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 ...
4
votes
2answers
120 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} ...
7
votes
4answers
752 views

How to collect terms with positive powers in polynomial

I am trying to collect all terms with non-negative powers of $x$ in polynomials like $\frac{1}{x^2}\left(a x^2+x^{\pi }+x+z\right)^2$ First expand the polynomial ...
4
votes
2answers
209 views

Alternatives ordering affects pattern matching in Cases?

Given expr = f[x, g[y], z] In the following query, the pattern h_[__, c_] appears as last slot in ...
1
vote
2answers
165 views

dropping a row with at least one value larger than a particular value

So for instance I have M X N table. I want to drop any row which has an element larger than, say, one in the second or the third column. I guess I have to do some sort of pattern matching. But not ...