# Tagged Questions

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

119 views

### Why the flat f[x] is treated as ghostHead_[f[x]]?

While reading this answer I feel confused. If we do not care any specific detail of the original question, then ybeltukov's answer essentially makes use of the following fact ...
182 views

### How to trim the zeros from the right of a list? [duplicate]

I need to remove the zeros from the right of an integer list up to the first non-zero element. Such as {0,1,0,0,2,0,0}->{0,1,0,0,2}. Padding zeros can be simply ...
1k views

### Finding the period of an array of integers

A simple array of integers is given. The problem is to detect if a pattern is repeatedly occurring in the array, and find the length of that pattern. For example, for ...
3k views

### Find zero crossing in a list

I'm looking for a function that finds the index of the zero-crossing points of a list. Before I go making my own subroutine to do this, I was wondering if anyone knows of any built-in Mathematica ...
92 views

### Can we say that “all functions in Mathematica are some kind of pattern-matching-and-replacement procedures”? [duplicate]

Currently I am studying Mathematica programming, and when I study pattern matching and replacement, I find it is quite similar to functions. So can we say "all functions in Mathematica are some kind ...
517 views

### Adapting “Find and Replace” functionality to work with Patterns

I was thinking if there is something like Find and Replace (Crtl+F) functionality adapted to work with patterns. Probably not, but it seems possible to create this with some effort and skills in <...
219 views

### Assumptions with patterns

I want that Mathematica assumes every symbol like Subscript[s,i] to be evaluate as a real and positive number. I have tried ...
123 views

### Is there a way to search for Arithmetic Progressions in a list?

If you have a list of integers is there a way of searching that list to see if there is a trend of Ax+B in the list? Not using all of the numbers, just seeing what trends like that are embedded in a ...
213 views

### How to highlight the elements in a list that match a pattern?

For example, {{1,2,3},{1,2,3,1,2,3,4,5}}with pattern {1,_,3}is transformed to ...
149 views

### DeleteDuplicates in a list of 2-tuples under condition

Having a list of 2-tuples, I would like to delete such 2-tuples that have 0 at second position, but only those, whose first element is not unique in the list. E.g. ...
335 views

### Matching pair of numbers {a,-a}, where a is numeric

Imagine you have a list of pairs of numbers, such as {{2,-2}, {1,5}, {1,-3},{-3,3}} The task is to reduce the given list to a list of pairs of type ...
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. ...
140 views

### How do I use ReplaceAll to replace strings of a specified form?

Why is "Xabcde" /. "X" ~~ e__ -> e "Xabcde" and not "abcde"
141 views

### Unexpected pattern matching behaviour: PatternSequence vs. Optional

fixed in 10.1 (windows) Consider the following pattern-matching expressions: ...
131 views

### Pattern matching with Complex. Feature or a bug?

fixed in 10.1 (windows) I have run into some strange behavior while doing some pattern matching. First, this works as expected: ...
4k views

### Looking for “Longest Common Substring” solution

I'm looking for robust code to solve the "Longest Common Substring" problem: Find the longest string (or strings) that is a substring (or are substrings) of two or more strings. I can just code it ...
50 views

### Matching x,y,z,2

I have a list of integers; I would like to replace anything of the form $x,y,z,2$ in such a list with $x+1, y+1, 0, 0$. The problem is that the $2$ may appear at the front, or in the first three ...
195 views

### Better output for NonlinearModelFit “ParameterTable”

The Standard table fo parameters of NonlinearModelFit is obtained from NonlinearModelFit[{{0, 1}, {1, 2}, {3, 3}}, a + b*x, {a, b}, x] %["ParameterTable"]] I ...
332 views

### Why can I not replace a Dataset using a rule?

Simple replacement of a Dataset object does not seem to follow the expected behavior... Dataset[{}] /. _Dataset->1 Returns the empty Dataset not 1 as I would ...
927 views

### Specifying string patterns in DeleteCases

It seems that DeleteCases is not compatible with string patterns, at least directly (see, for example, this question). Is this true? If so, why is this the case? ...
53 views

### Selecting from a list [duplicate]

OK, I know this must be a simple problem, but right now I'm just stuck and need some advice with this :). I have the following list: ...
74 views

### ReplaceRepeated made a single replacement where I expected multiple replacements to be made

This seems like a very simple action: {a, b, c, d, e, f} //. {r___, x_, y___} :> {r, 1, y} but it replaces only the first element giving ...
475 views

I have a list of strings and I would check if there is an empty string element, that's "", because I need to replace it with a "0". I try the following ...
45 views

### FirstPosition returning an error message together with the correct answer

I have the following code: ...
41 views

### How do I match all the subscripted terms in Times?

Suppose I have an expression: $W = A_{i,p,q...}\,\, a_ia_ja_ka_l...$, where $A_{i,p,q...}$ is an expression that does not depend on $a$, the indexes $i,j,k,l,p,q...$ are integers and all the integers ...
153 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 NumberQ...
297 views

### How to search for patterns to find the positions of prime numbers

I have a summation which yields a prime number at each location there is a 2, and I do not know how to search for the 2's. ...
179 views

### Extracting numerical coefficients from an expression

I have very large expression and I want to extract and sum up all the numerical coefficients which multiply the summands. For example, expr = x + 2*y + 3*z*w ...
190 views

### Change matrix elements at specific locations?

Let's say I have an array a={{1,2,3}, {4,5,6}, {7,8,9}} I want to have all elements along the diagonal multiplied by 2. ...
522 views

### Determine if all the zeros in a list occur at the end

I have a collection of (short) lists of nonnegative integers. For each, I would like a predicate that decides if all of the zeros in the list appear at the end. For example, ...
163 views

### Can a pattern examine all partitions of a sequence?

Say I have a list: {a, b, c, d}. I'd like to check that the list has some partition, say {{a, b, c}, {d}} such that all the elements of the partition satisfy a ...
144 views

### Replace elements that match pattern

I am using pattern matching to identify elements in a list to be replaced. How can I supply a list of patterns to match and replace all elements in the list that match the pattern? The problem I have ...
100 views

### Removing characters from non-strings

I have a large list of lists that contains mixed data, some real, some strings. The lists are of various lengths and depths. Some of the real data values have an asterisk appended to them, e.g.: <...
114 views

### Compare tree structures in mathematica

Since Mathematica expression is basically a tree structure, I would like to perform tree structure comparison with certain restrictions, for instance that the identity of nodes on the same level be ...
317 views

### Why these ways of defining a function with variable number of arguments fail?

First: I know about the correct way to define a function with variable number of arguments: Clear[f] f[s__] := Plus[s] f[1, 2, 3, 4] (* 10 *) BUT I ...
77 views

### How to create a general expression for an integer derivative?

I need MMa to return a general expression for the jth derivative wrt v of v^n. This didn't work: ...
83 views

### How to use pattern matching for integral identities?

I have an unknown pdf f[x], and I need to express integrals involving f[x] as expansions of the moments of f[x]. For example: ...
186 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. ...
75 views

### FilterRules with pattern for name [duplicate]

I have a list of rules and I want to filter it using a pattern for the initial string representing the name of the rule. So that in the example below it filters linearBool even if it is called "linear"...
122 views

### Odd behavior matching powers of pi

I have a long list of generated values from which I want to remove "weird" ones like Sin[Sin[1]] and Pi^2/4. However, trying to ...
265 views

### Pattern matching multiple symbols names and powers

Seemingly a relatively simple problem, I can't seem to find a solution... I want to build a pattern that will match any symbol whose name starts with V, and is elevated at any power. Something on the ...
609 views

### NotebookFind and String Pattern Expressions

Is there a way that NotebookFind can be used to match string pattern expressions rather than just strings? The documentation for ...
680 views

### Best way to modify values in a list of rules?

Recently I had to solve a problem similar to this: Let's say I have a list of list of rules ...
202 views

### How can I improve NumberString?

I would like to test strings to see if they represent numbers. This should include number representations with precision marks and scientific notation. NumberString ...
117 views

### Selective deletion of nested list elements centred around a certain value

I have a list which looks like: ...
62 views