Questions tagged [filtering]
Questions on filtering or selecting data based on certain criteria. This is to be used with primary tags such as list-manipulation, string-manipulation or signal-processing, with the primary tag indicating the specific use case.
717
questions
11
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234
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Classifying elements, by the value of a fixed function, using Replace
Let L be a list of several lists. And the length of each list is less than 1000.
You can create L by
...
- 2,451
1
vote
0
answers
71
views
sometimes Select / sometimes Position is faster
As you see,
For list L,
L1(Select method) is slower than L2(Position method).
But for list <...
- 2,451
1
vote
2
answers
172
views
How to pick lists to satisfy a given form?
I have a list of the following struture:
(my real list also has the same structure, just much longer not just 12)
...
- 1,656
1
vote
0
answers
22
views
TreePosition with multiple (not just node data) conditions
Given a Tree object, TreePosition takes patterns only on the "data" of the node plus a level spec.
...
- 3,720
0
votes
1
answer
65
views
get positions satisfying multiple criteria
Given a list L.
It is mathematically proven that there is no element in L matching 2 or more patterns in ...
- 2,451
3
votes
2
answers
88
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How to remove duplicates from a pair with some conditions?
Here is a simpler example of my real problem.
Assume that I have a groups which includes sublists as follows:
...
- 2,147
3
votes
1
answer
69
views
Select with simplification does not work
Given a list, I want to find all elements that have positive imaginary part.
For example, if $y,z\in\mathbb R$ and $a>0$ and the list is $\{ ia+y, -ia+z\}$, then the result should be $\{ia+y\}$.
...
- 909
0
votes
0
answers
47
views
How to DeleteDuplicates from a list of Rules having set to different values whereby we wish to drop the last occurrence?
About This Function
This will eventually set default values for Options based on the end users preferences so that no OptionsPattern need ever be set. The symbol<...
- 1,647
1
vote
1
answer
49
views
Sorted Tuples without Filtering
Say I have a list $L$ where the elements can be sorted into some canonical order. I want to use Tuples[L,m] but I only want the output lists to be sorted and ...
- 45
0
votes
1
answer
26
views
Exclude blank values from dataset (GeoPosition)
Any idea how to filter this dataset to exclude blank values in FlightPath?
1
vote
2
answers
76
views
How to filter out the elements that meet the requirements [closed]
How to filter out the elements {a,b,c} to form a list that meet the requirements 0 <= a <= 1 && 0 <= b <= 1 && 0 <= c <= 1? I used Cases, but the result is not a list....
- 1,365
2
votes
2
answers
56
views
0
votes
1
answer
88
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Compute the sum of digits of very large integers via table and filtering
I am trying to find the smallest multiple of 2022 whose digits add up to 2022. So I built a table of such numbers, then trying to see which cases pass. This number will obviously have at the very ...
- 389
1
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2
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34
views
Select with a variable in the condition always returns the empty set
Mathematica beginner here.
I have a function that picks indices based on the value of a passed variable x. This works fine when a concrete value is picked for the variable:
...
4
votes
2
answers
267
views
List letters at even- or odd-numbered positions in Alphabet
To make a list of the letters at even-numbered position in Alphabet, I wrote this code:
Select[Alphabet[], EvenQ[Flatten[Position[Alphabet[], #]]] &]
But it ...
- 173
4
votes
3
answers
128
views
Change a group of values in a list of association
Noob here.
I want to change the value of all the keys "e", that meet my filter criteria ("c" and "d" are above or equal 20).
...
- 75
2
votes
2
answers
91
views
2
votes
3
answers
104
views
Selecting patterns
I have data as a list of four element lists, some with missing data, thus
...
- 579
0
votes
0
answers
34
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Chebyshev I LPF filter phase shift
I'm trying to design a Chebyshev filter with zero phase shift but I'm doing something wrong here and it would be great if anyone can point me the right way. My Functions are:
...
- 317
2
votes
1
answer
64
views
Select data based on string pattern
I'm trying to select data from nested lists based on seconds.
This is my data:
...
- 327
5
votes
2
answers
167
views
Select behaving differently with Dataset and List
I have just encountered what I would term an unexpected disagreement in behaviour between Dataset and List. Consider the ...
- 4,677
1
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0
answers
75
views
Using multiple criteria with Select [closed]
Suppose I have this list of strings...
test = {"abc", "abcdef", "ghi", "jkl"}
...and wish to filter it, selecting only ...
- 3,446
2
votes
1
answer
54
views
Cases with condition and two different outcomes
Given
t1 = {{{{3}, {2, 5}}, 1}, {{{3}, {2, 7}}, 5}, {{{2, 7}, {3, 7}}, 7}, {{{2, 7}, {3, 5}}, 1}}
I want to double the first part if only one number is present ...
- 2,020
3
votes
1
answer
47
views
Delete/Drop nested columns within dataset
I have sorted some data into a dataset, but when exporting the dataset to be an external file I would only need certain columns within the dataset. I would like to drop the everything within the "...
- 73
1
vote
1
answer
51
views
selecting specific part of data set [closed]
I have data set in form {section, Arcangale ,X,Y, type}. Section is the number between 1 to 3 (1,2,3), Arcangale is number change from 0 to 1 something like this (0.0176575), x and y are coordinate (...
- 383
0
votes
1
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55
views
Check if a fraction leads to an integer, choose $r$ and run trough $0\le a\le n$ and go to $r+1$
Well, I am trying to do the following: I have two functions $y(r,a)$ and $z(r,a)$ and I want to check of the division of both those functions leads to an integer. In order to do that I want to choose ...
- 1,723
5
votes
1
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134
views
How can I remove First[{}] from the output list of a function?
Consider:
listOfKeys = {"Ambientalismo", "Anoressia"};
list2 = First /@ (WikidataSearch /@ listOfKeys)
I've tried
...
- 518
1
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0
answers
49
views
1
vote
0
answers
58
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Select n elements of the list [closed]
I have a list of elements
data = {-0.023504, -0.022846, -0.022846, -0.025479, -0.025479, -0.024821,...}
The list consists of 20000 elements.
How to select first ...
- 301
4
votes
3
answers
145
views
Mathematica edit list elements
I wanted to delete pair with the same argument and leave the pair with the lowest value, for example we have list:
...
- 301
4
votes
1
answer
151
views
How can I speed up processing with DeleteCases?
I would like to get points that are only inside a region. Here are the region and unfiltered points:
...
- 2,977
7
votes
1
answer
138
views
Pick with Unitize vs Pick with Clip vs Compiled Select speed - anything faster?
Given a large list of $n$ dimensional sublists where each sublist has integer elements I am trying to find the quickest way of finding all sublists that satisfy some constraint on their elements.
A ...
- 485
0
votes
1
answer
80
views
How to create a dataset out of the entities?
I am working on learning how to create a dataset from a series of entities.
I have the following function that finds all properties of a certain entity:
...
- 1,037
0
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0
answers
32
views
5
votes
1
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122
views
5
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1
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123
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How to access a Dataset column via a variable
I want to pick values of varying columns from a dataset, eg. from the Dataset in the documentation
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- 5,453
1
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0
answers
73
views
How to test for arguments for a pattern that is of a positive Integer OR Infinity so that both filter through to the definition on RHS?
How can I filter an argument of a function so that definition works on positive Integers (y >= 0) or Infinity? It will ...
- 1,647
3
votes
1
answer
42
views
Multicriterial filtering operators in Datasets
How to generate a long Select query with Dataset-based syntactic sugar? For instance, let we generate the dataset
...
- 1,730
0
votes
0
answers
43
views
List with unknown dimension
I have a long list of lists, called Evlist in the following example, which I have to extract information from to be put into new lists Ev and w. I do this with the following code:
...
- 189
0
votes
0
answers
44
views
Solving a system of equations (works with squares not with fifth powers)
Well, I was trying to solve a system of equations in a different question of mine.
There @kglr gave a very efficient code for solving that system of equations using squares:
...
- 1,723
3
votes
1
answer
83
views
Removing a element from list when obeying a certain condition
Well, I have the following code:
Select[PowersRepresentations[n, a, b],
DuplicateFreeQ[#] && ! MemberQ[#, 0] &]
This code finds ...
- 1,723
3
votes
1
answer
58
views
select subset of combinations based on condition
My question is about choosing a subset of combinations within a list, based on a condition.
Fot example, a shop sells 26 products. The name of a product starts with a letter. Each product has a price. ...
- 2,371
1
vote
1
answer
45
views
remove erroneous values from array
I have a set of squares arrays (images) of values -100k to 100k. Occasionally the camera that generates the images has a readout error and reads an extremely high value (in the 10e30 range). These are ...
- 147
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0
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66
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how to run multiple notebook at the same time using multiple kernels
My problem is that the second notebook file opens but waits for the first notebook to be evaluated. I want to execute both file1.nb and file2.nb at the same time. Here is my code.
any idea?
...
2
votes
2
answers
203
views
Why does GaussianFilter not have a periodic option?
Let us say I have a table:
tab = RandomReal[{-1, 1}, {128, 128}];
I can filter it using GaussianFilter as follows
...
- 21.7k
1
vote
2
answers
63
views
Replacing data in a new table using the index
This problem might be similar to others but I could not find the solution with the extra step I need.
I have two tables with the same value on the x axis, and different in the y. I want to pick values ...
- 81
2
votes
1
answer
113
views
How to separate these circle based on their pixels mean intensity?
I have this image I want to separate green circles from yellow circle in two different images whiteout changing the pixel intensity information. I used the mean intensity
...
- 23
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0
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3
votes
1
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