# Tagged Questions

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

53 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: ...
172 views

### Pick bug? level 0 matching

A previous discussion of this issue (Is there a bug in Pick?) accepted that matching at level 0 is not a bug in Pick. Was that correct? I am not yet persuaded. ...
487 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 ...
491 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 ...
69 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: ...
605 views

### Find patterns in a list

again, I have a list like this: ...
434 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 , ...
214 views

### Isolating string characters

I have the following string: ...
83 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 ...
133 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 ...
149 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. f g+ Dt[f, t] g +Dt[g, {t, 2}] f What I would like to ...
232 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 ...
71 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 ...
186 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 ...
535 views

### Using ReplaceAll to replace a head

Why would this work to replace the head b with newHead: ...
175 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 ...
47 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: ...
69 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 <...
297 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 \$f(a,b,c;...
97 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: ...
516 views

### MatchQ-ing Associations (MMA 10)

Consider {x->1} which has FullForm List[Rule[x, 1]] and, therefore, ...
107 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 ...
283 views

Question2:: ...
34 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 ...
62 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 ...
238 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: ...
208 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 ...
310 views

### Mma10 mystery: Failure of pure function substitution with Interpretation?

Bug introduced in 10.0.0 and fixed in 10.0.1 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 ...
141 views

### Get part of lousy data

I want to get part of large data. some part of this data is as follows: ...
127 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 {"10....
126 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 ...
177 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 ...
582 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 ...
274 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 ...
1k 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 ...
235 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 ...
229 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 ...
131 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 ...
98 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 ...
152 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: <...
176 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 ...
234 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 ...
211 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 ...
132 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 ...
48 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 ...
212 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 ...
97 views

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

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 ...
162 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 ...
66 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 ...
561 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 ...