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

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1
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1answer
32 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
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2answers
136 views

Using ReplaceAll to replace a head

Why would this work to replace the head b with newHead: ...
8
votes
1answer
80 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
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0answers
36 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
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1answer
31 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
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2answers
48 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 ...
2
votes
1answer
68 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: ...
11
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1answer
163 views

MatchQ-ing Associations (MMA 10)

Consider {x->1} which has FullForm List[Rule[x, 1]] and, therefore, ...
2
votes
2answers
113 views
0
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0answers
26 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
2answers
156 views

Why wouldn't ReplaceAll (/.) work with this list of number? [closed]

The answer to this might be simple, but why would ReplaceAll return such a weird result when replacing a number in a list of numbers: ...
3
votes
1answer
56 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 ...
8
votes
1answer
128 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
158 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 ...
5
votes
1answer
222 views

Mma10 mystery: Failure of pure function substitution with Interpretation?

I had code to display with subscripts from Displaying index as subscript on output: e.g. C[i] -> C_i with Notation[...] or Interpretation[..]? which is now breaking an innocuous pure function ...
4
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2answers
134 views

Get part of lousy data

I want to get part of large data. some part of this data is as follows: ...
0
votes
3answers
75 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 ...
1
vote
2answers
81 views

Cases do not return all expected result

I have the following line code: Cases[g[h, r, t, b, m], x_[__, y_, __] -> y, {0, -1}] I am expecting the results to be ...
3
votes
1answer
79 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 ...
13
votes
1answer
275 views

Quick way to use conditioned patterns when defining multi-argument function?

I have a simple function that is supposed to only accept numeric values (i.e. complex/real numbers and constant symbols e.g. Pi, E). $$f(a,b,c)=a+b+c$$ Edit: I should have chosen a less simple ...
5
votes
3answers
153 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 ...
8
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8answers
832 views

How can a power of 0 or 1 be replaced?

Consider this given example for ReplaceAll 1 + x^2 + x^4 /. x^p_ -> f[p] This returns ...
5
votes
1answer
213 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 ...
4
votes
2answers
175 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 ...
2
votes
2answers
96 views

how to take some parts of String with certain pattern

I have the large number of files in which the file's names follow certain pattern. for example here are names of two files ...
2
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2answers
77 views

Find names similar to a given name in a large data set

I'm trying to find a 'similar' name to every item in a list ...
3
votes
1answer
85 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: ...
0
votes
2answers
58 views

Searching for phrases in a block of text

One could call this a pattern finding question with dictionary (or WolframAlpha) lookup, but let me give you some background first. I have a couple of friends who are trying to improve their English ...
8
votes
1answer
100 views

CSS Selectors for Symbolic XML

Symbolic XML is a convenient way of managing XML in Mathematica, at least for casual use or small tasks. Here and elsewhere you can find examples of XML handling in Mathematica, including XSLT/XPath ...
1
vote
2answers
114 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 ...
1
vote
2answers
48 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 ...
1
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0answers
43 views

Placement of pattern matching rules in functions [duplicate]

Is there any difference at all between f[x_Integer /; x >= 0] := x + 1; f[x_Integer] := x - 1; f[x_] := Null; and ...
3
votes
1answer
82 views

Custom operators; custom pattern matching with pure functions

What I'm trying to achieve in Mathematica is the creation of a binary operator whose operands are both pure functions over the natural numbers. The result of the operator should be another pure ...
3
votes
1answer
80 views

How to localize symbols on the right-hand side of Rule when using ReplaceAll?

I am frustrated by the following: {1, 2, 3.0} /. a_Integer -> a + 1 The a on the left side of the arrow is localized and ...
0
votes
1answer
111 views

Extracting graphics primitives from a Graphics expression with ReplaceAll

If we have a graphics object, plt = Plot[Sin[x], {x, 0, Pi}] and we need to retrieve the discrete point data from it. This can be easily done by using ...
0
votes
0answers
38 views

Hashing by Equals instead of SameQ

I have some numerical code involving complex numbers representing points on a plane. Some of these are equal but not identical, ie ...
4
votes
3answers
410 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 ...
2
votes
1answer
47 views

StringExpression: pattern reapeted one or more times matches pattern repeated zero times

I try to construct patterns using Riffle and Except StringExpression@Riffle[{"a", "b", "c"}, Except[{"=", ","}] ..] and expect it to match "a_b_c", but not ...
3
votes
1answer
121 views

Why even try the semantic constraints, if expression can't match the pattern structure?

This result is unexpected: Trace[MatchQ[{7}, {_?NumberQ, __}], NumberQ] (* -> {{NumberQ[7], True}} *) Why evaluate ...
3
votes
2answers
96 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 ...
3
votes
3answers
146 views

StringCases using RegularExpression fails when there is missing data

I got some text scraps with this structure "Focal Plane: 198' Active Aid to Navigation: Yes *Latitude: 35.250 N *Longitude: -75.529 W" But some of them lack ...
4
votes
1answer
85 views

Pattern matching and HoldForm

Create rules based on data. I have a system that picks out on date,based on some rules. I then want to generate a new rule based on this date and apply the rule to a new dataset. ...
2
votes
1answer
87 views

What is the proper way to the pattern form Repeated in my code?

I'm matching a pattern with Repeated (..) How can I use the repeat count in the replacement rule? Example: ...
0
votes
1answer
70 views

Sum similar elements [closed]

I am interested in summing elements in a list or sublist that are similar. I want the sublists of my second elements to be added cumulatively only if their first elements are the same. This is my ...
20
votes
4answers
930 views

Detecting patterns of black and white stones on a 2D board

I'm writing a program to play a game of Pente, and I'm struggling with the following question: What's the best way to detect patterns on a two-dimensional board? For example, in Pente a pair of ...
0
votes
1answer
74 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 ...
0
votes
1answer
62 views

Pattern matching with PDF, Distributed and multivariate distributions

I have defined a function to compute the Shannon entropy of a probability distribution: ent[p_] := Expectation[-Log[PDF[p, x]], x \[Distributed] p] This works ...
3
votes
3answers
96 views

Name scope confusion

Sorry for the too ambiguous title. First consider a following code snippet. ...
4
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4answers
420 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 ...
1
vote
1answer
67 views

How can I get the functionality of a command ReplaceAllList?

I'm trying to use ReplaceList to match subexpressions. I expected the command: ReplaceList[{p, {p, p}}, {x_, y_} -> x y] to output two results, equivalent to: ...