# Tagged Questions

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

228 views

### Strange behavior with Cases and Position with SetDelayed

I feel like I must be missing something simple and obvious here, but this has me scratching my head. This works as expected: ...
212 views

### ReplaceAll problem

Bug introduced in 10.1 and persisting through 10.2 or later Confirmed, as bug, by WRI: [CASE:3402234] I am trying to combine terms of the type ...
77 views

### Patterns with inactive integrals

I am trying to do algebra on unsolved integrals but not getting the pattern-matching right. I want the correlation of f[x] and f[x]+a*d[x], normalized by their self correlations. ...
131 views

### Matching Symbol or Subscript, but not Symbol arguments of Subscript

I'm trying to get a list of all the variables in a symbolic expression. Some are named with Symbols, some are named with ...
234 views

### Cases vs Select, Pattern vs Pure function [duplicate]

What is the difference between having Cases with selection condition presented by pattern and a with pure function as condition? ...
147 views

### Select largest number using pattern

I have the following expression: myExpr=R[C[2],B].(II+R[C[3],C[2]].(II+R[C[4],C[3]])) I need to create a pattern which would replace the ...
100 views

### How to compare and remove x-coordinates (and the associated y-coordinates) that are less than previous x-coordinates?

I am using Mathematica version 9.0 and am trying to compare and remove x-coordinates, and the associated y-coordinate, that are less than previous x-coordinates. Below is an example using sample data. ...
35 views

### How to pick max/mins of elements that match patterns?

I have a list of complicated expressions that involve indexed coefficients. For example: expr={m[5],c[3]*m[1]^2+m[2],Sqrt[m[2]+3*m[3]*c[8],foo[m[3]*m[5]]}; How ...
264 views

### Replace matrix rows conditionally while avoiding For loop

I have the following variables: myMatrix={{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0},{0,0,0}} myIndices={1,3} I need to replace the rows ...
72 views

### Confusion over blank sequence in pattern matching

My overall goal was to produce a list of heads used in a graphics output. For an example I used: ...
159 views

### Find position avoiding For loop

I have a list: {a,b,c,d,e,f} And a function sizeFunc[element_] which returns the size ...
67 views

### Dropping rational coefficients

I have a list of expressions (they all are exact numeric quantities, not containing any variables), some of them have integer or rationals coefficients, or complex coefficients with rational or ...
78 views

### Trouble simplifying using Replace

I have the following expression: w.a.b.r+w.c.d.r I want to get: w.(a.b+c.d).r So far I used ReplaceRepeated: ...
256 views

### Help with PatternSequence

I have a list of strings of the form list = {str1, str2, strx, str3, .., str10} each string contains both letters and numbers, except for ...
163 views

### An equivalent to Condition that I can use anonymously when string pattern matching

When I name a pattern I'm working with, that name stands for the same particular expression wherever it shows up. That's a basic precept of how the Wolfram Language's pattern-matching works. But if I ...
182 views

### Match a variable name pattern [duplicate]

I have a list of variables: {RBI,RCD,ASD,FGH} I want to select only those whose name starts with R. Using the pattern Rx_ ...
298 views

### How to identify all rules that match pattern type? [duplicate]

I would like to be extend the below solution to be able to find get all rules from the list step[2] that match the generic pattern k_Digit_p. Where k and p are not ...
60 views

### How to use EvenQ[] in patterns? [duplicate]

This works: (w[1] + w[2] + w[3]) /. w[s_] -> If[s == 2, w[s], 0] (* w[2] *) This doesn't: ...
149 views

### How to Negate a Pattern Test and Transform a List of Strings to a JSON array

First I would like to find out how to negate a pattern and based on this I would like to solve this little problem on how to transform a list of strings to a JSON array. This is how I started working ...
106 views

### Delete Element within a List based on the Order [closed]

I want to do the following, deleting the element of a list that do not match an increasing order as example: {1,2,3,4,6,5,7,8}->{1,2,3,4,6,7,8} I've thought of using DeleteCases but I'm not able to ...
407 views

### Opposite of Alternatives

I was looking at this question (here) and I tried to find any thing gives the opposite of Alternatives. In other words, some pattern matching function that gives ...
342 views

### Is there a GraphicsPrimitiveQ (or a complete list of Heads of graphics primitives)?

For various reasons related to workflow associated with creating figures for journals, I am creating functions that will accept graphics primitives and a set of options and spit out a ...
197 views

### How to make a function that yields a number under power operator by using pattern matching?

Can I ask you a question related to function and pattern? I would like to make the function below work which doesn't yield return values I expect. How can it be done? ...
188 views

### Is there any way to use head of Real and Integer altogether?

Is there any way to use the head of Integer and Real together like below? The below is not right, I know that, it is just for ...
149 views

### Why is there a difference when formulating patterns for Select and FirstPosition?

Select[{1, 2, 4, 7, 6, 2}, # > 2 &] Gives {4, 7, 6}. OK! So one should think that the following would work: ...
56 views

### Remove cases where region specified incorrrectly

I am using MeshPrimitives to get a list of 3D components of a Mesh Region. Within that list, I normally get some incorrectly specified regions, such as ...
144 views

### How to debug this failing pattern-matching expression?

NB: this question is primarily about troubleshooting and debugging, and only secondarily about pattern-matching. IOW, I'm far less interested in getting an explanation for the situation described ...
96 views

### Strange result of DeleteCases in an association

The function DeleteCases can be used for associations, also with level specification. Here is an example where some values are associations: ...
121 views

### Using MapThread over 2 lists different length with criterion on minimal differences

Say I have 2 lists ...
404 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 ...
128 views

### Is there an elegant way of delaying evaluation of A==B when calling a function that uses this pattern

Suppose I wanted to define a number of functions that accepts expressions of the form: ...
77 views

### What is the role of the pattern object in this implementation?

In the documentation I found a nice idiom which allows me to do model fitting with interpolating functions. I think this kind of thing is amazing and a credit to the utility of an environment like ...
78 views

### How to exclusively match in the numerator?

Here is an expression (one of many) that involves two complicated terms: \begin{multline}\text{expression} = \frac{\log \left(\frac{c}{d}\right) \left(2 a d F(a,b,c)+a^2 \left(a^2-2 a (b+c)+b^2+4 b ...
917 views

### How to define a recursive pattern?

I want to translate this recursive syntactic definition into a Mathematica pattern1: $$\mathtt{x}: \begin{cases} \text{Null}\\ \{\textit{integer}, \mathtt{x}\} \end{cases}$$ In other ...
58 views

### Why has FreeQ a quadratic complexity with high depth?

I am a little puzzled by the following test: ...
196 views

### Two ways to speed up slow Integrate[]s? (Can't do either)

I run into problems like this all the time on the complicated integrands I pass to Integrate. The following code works but takes a veeery looong time: ...
153 views

### Confused by the opts : OptionsPattern[ ] pattern

I'm trying to make sense of the syntax in the clause opts:OptionsPattern[], as found in this standard "rule-based" (pseudo-)function definition pattern: ...
41 views

### What does __Rule do in Mathematica? [closed]

What does __Rule do in mathematica? I understand the __ is used for any repeated expression, but why is the Rule appended at the end? For example: Import nested JSON file Thanks!
129 views

### Match groups in regular expressions

I'm trying to understand Mathematica's pattern matching in strings, but I have some doubts. 99% of the time I need to a) check if a match occurs and b) retrieve the matched patterns. I come from ...
117 views

### How to Pattern Match complicated patterns? [closed]

How can I get the output expressed in terms of p1 and p2 instead of exponentials? ...
116 views

### How to write a pattern that matches all functions

What is the correct way to match a function in an expression in the way that Cases[Sin[x] Cos[x], _Sin | _Cos, {0, Infinity}] matches ...
73 views

### Ordering in noncommutative multiply

I have an expression like s ** p1 ** p1 ** p2 - s ** p1 ** p2 ** p1 Which should be zero because the commutator between p1 ...
124 views

### How to apply ReplaceAll to denominator?

Here is the simple task. In reality, it's far more complicated, but it comes down to this. I want to take the expression $\frac{y}{x^2}$ and replace $x^2$ with $k$. This doesn't work: ...
104 views

### Pattern matching list of elements with different heads

I have a function, which I want to accept only a list of kind of elements belonging to a group. The task comes down to finding an elegant pattern suitable for easy to read function prototype. As an ...
60 views

### Emulating Case Pattern replacement

As most regular users, I have developed utility functions complementing the Wolfram language for frequent tasks. In particular, I have variations on Cases (see ...
203 views

### Sow only if different from zero

I am trying to collect elements with Reap and Sow, where I am interested only in non-zero elements, that is I am trying something like that ...
87 views

...
41 views

### Where can I find mathematica documentation about @@@? [duplicate]

For example, to build a rule from 2 lists {a,b,c},{1,2,3},I use : Rule @@@ Transpose[{{a, b, c}, {1, 2, 3}}] : {a -> 1, b -> 2, c -> 3} OK, but how @@@ works ? (Black magic for me) I am using ...