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.
780
questions
3
votes
1
answer
55
views
Can you not use And[] inside a Select[]?
I have a list of lists of integers that are each sorted numerically. Here is a sample of it: {{2, 8, 9}, {3, 7, 9}, {4, 6, 9}, ...}. I wish to only pick out members ...
- 347
0
votes
0
answers
50
views
Comparing graphs in mathematica: shape vs. name
I'm trying to identify and remove duplicate graphs when contracting vertices. To illustrate this, I'll start with two simple graphs where I'm trying to create a function that can recognize them as ...
- 2,678
7
votes
7
answers
406
views
Merging and keeping only the sublists whose first two elements are equal
I have a list containing sublists.
...
- 844
6
votes
1
answer
238
views
5
votes
6
answers
129
views
Extracting up to $n$ elements after a specified marker from a list
I have a list from which I need to select up to two elements that follow each occurrence of a marker.
For example, the selected marker is ...
- 4,313
5
votes
2
answers
271
views
Express a "not equal to A or B" criterion in Select
I have a list of pairs of strings: myPairsList. I wish to Select all the pairs that do not contain ...
- 10.2k
3
votes
5
answers
466
views
How to find the most repeating row?
Consider the following table:
tab={{1,0,0,1},{1,0,0,1},{0,1,0,1},{1,0,0,1},{0,0,0,1},{1,0,0,0},{0,1,0,1}}
Could you please tell me whether there is a command which ...
- 4,984
4
votes
4
answers
332
views
1
vote
2
answers
97
views
How to extract the following data from the file?
Consider the following file. It has the form
...
- 4,984
13
votes
13
answers
818
views
Select from list elements greater than next element
Given
t1 = {3, 2, 8, 6, 1, 9, 4, 1, 5, 0}
I want to get all the elements which are greater than the right neighbor. The result would be
...
- 2,304
4
votes
8
answers
466
views
How to get a Table of pairs (a/b, c/d) where GCD[a,b]==1 and GCD[c,d]==1?
I am trying to make a Table pairs of (a/b, c/d) where GCD[a,b]==1 and GCD[c,d]==1. I have tried the following:
...
- 844
1
vote
2
answers
60
views
Selecting interesting graph positions with a button press/click or something similar
Assume that I have a graphList as shown below (a simple working example).
...
- 2,361
2
votes
2
answers
88
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Looking for solutions to filter out one-sided angle pairs in line intersections
I posted something here a while ago, but I think it's a bit messy and difficult to understand. So, I'll create a new post to explain the concept and what I want in a different way, hopefully making it ...
- 2,678
6
votes
7
answers
593
views
Dropping disordered numbers in a list
I have a list of numbers like
l1 = (1,2,3,4,8) and clearly, l1 is in order (next number is greater than previous number).
Well, ...
- 405
9
votes
4
answers
2k
views
Find Roman numerals up to 100 that do not contain “I"
The question is from Elementary Introduction to the Wolfram Language, section 28 Tests and Conditionals: Find Roman numerals up to 100 that do not contain “I”.
What am I doing wrong that the following ...
- 417
1
vote
1
answer
58
views
Sumif and delete cells in Mathematica
I want to create a simple "sumif" formula like in Excel. However, I am desperate since I cannot achieve a result.
First, I am importing an excel file with lot of datas.
data = Import[
"...
- 11
3
votes
6
answers
676
views
Make a list of the first 100 primes, keeping only ones whose last digit is less than 3 [closed]
This is a question from an "Elementary Introduction to the Wolfram Language" Section 28: Tests and Conditionals. We are asked to "Make a list of the first 100 primes, keeping only ones ...
- 417
2
votes
3
answers
315
views
Finding transitive Boolean matrices
I am fairly new here and with Mathematica too.
I have a question regarding Boolean matrices but before this I did a random search and got this
Defining an arbitrary binary relation
But I am unable to ...
- 55
9
votes
4
answers
602
views
Check if a string is a date
I have a list of strings,
{"BD4675365", "Corp", "Managers", "Syndicate", "2021-03-08", "8434926"}
and I ...
- 1,937
2
votes
1
answer
49
views
How to select only particular values from the list using dialog windows?
Consider some list:
list = {"A","B","C","D"}
How to select only particular values from it using a dynamic dialog window ...
- 4,984
5
votes
3
answers
263
views
How can I select only rows where a column is equal to any value from some list? [closed]
Consider some data
data=Table[{RandomInteger[{0,10}],RandomReal[{0,1}]},10];
and some list
list={0,5,7,3};
How can I leave ...
- 4,984
1
vote
0
answers
49
views
Selecting elements with a particular slope
I have a dataset for which I want to identify 'groupings' based on three criteria, but only one of them is giving me a headache. The criteria are that each group must:
have a minimum number of points ...
- 1,396
1
vote
2
answers
64
views
How to leave only the columns satisfying the following condition?
Consider the following pre-generated table:
...
- 4,984
0
votes
0
answers
41
views
Optimization of conditions applying
Let we have some data generator, e.g. lazy tuples or permutations.
I need to select data by some conditions cond1, cond2, …, up to 5-6 conditions.
All of them need ...
- 1,085
0
votes
0
answers
42
views
Speed up Select Operating on a Large List with Multiple Criteria
I am using the following code to select stocks that have performance data starting before one specified date and ending after a second specified date, as follows:
...
- 1,294
9
votes
6
answers
722
views
Can I tell DeleteCases not to delete function arguments?
Given list = {1, 2, f[3, 4], {5, {6, g[7, h[8, 9]]}}, {f[10], 11}};
I want to get
{f[3, 4], {{g[7, h[8, 9]]}}, {f[10]}}
just ...
- 5,562
1
vote
2
answers
57
views
How to make lists all the same length by automatically removing every second element?
I have 20 files of matrices which all contain the same kind of data. I can import and take the single column I need out of every file into a list. I need to average each of the 20 file's lists ...
- 31
2
votes
1
answer
121
views
2
votes
2
answers
108
views
Remove sublists with duplicate elements within
I have this list
DeleteDuplicates[Sort[#] & /@ Tuples[Range[4], 3]]
which gives me
{{1, 1, 1}, {1, 1, 2}, {1, 1, 3}, {1, 1, 4}, {1, 2, 2}, {1, 2, 3}, {1,
2, 4},...
- 426
6
votes
3
answers
292
views
Apply pattern using a Slot (#) to each list element using a second slot
I am trying to find a neat way of applying an operation to each list element, but do not know how to properly use multiple slots or whether it is actually possible to solve this with multiple slots.
I ...
-1
votes
1
answer
67
views
How to Paste Complex Transfer Function Equation to Excel [closed]
I am trying to paste this transfer function to Excel, is it possible?
5
votes
4
answers
177
views
Filtering out function pairs with domains lying on one side (left or right) of an intersection point
I have a list of pairs of functions that intersect at one point, as shown in the image. I am attempting to remove pairs where the domain of both functions in the pair lie on one side of the ...
- 2,678
5
votes
3
answers
272
views
Delete first case
How to delete just first occurrence of given value from a list?
Without sorting etc.
Something like this:
...
- 1,085
4
votes
2
answers
307
views
Why does Select not work here?
Why does this not work? It returns empty while I expect the first two elements are selected.
...
- 431
0
votes
1
answer
53
views
What's the expression of transformation T in area-based Image operations such as ImageFilter and ImageConvolve?
in the “tutorial/ImageProcessing”, as the following picture shows
I just wonder what's the expression of the T in the area-based image operations such as ...
- 343
4
votes
2
answers
117
views
How to discard the repeating elements of a list [closed]
Lets say there is a random list of expressions :
a={Sin[x], Sin[3 x], Sin[4 x], Sin[x], Sin[4 x], Sin[x], Sin [5 x], Sin[3 x], Sin[5 x]}
Plot[{a}, {x, 0, 2 Pi}]
...
- 811
1
vote
1
answer
50
views
How to convert or filter a comma-numbered elements in a data to number as elements in filtered data?
My subset data (10 Rows, 3 Columns) of the big data looks like this:
...
5
votes
5
answers
185
views
How to select elements from a list of pairs based on first element belonging to a different list?
This is my very first question and I really appreciate this ability and thankful the community.
I have two lists and need to select only those pairs from the first list, first element of which is ...
- 107
0
votes
3
answers
72
views
Use the command Select to find all integers x in the list $r=Range[16]$ such that $Mod[x^4,17]=-1$ and also try doing it by cases command
My try:
r = Range[16];
Select[r, Mod[x^4,17] = -1]
but it doesn't work.
How can I do it?
- 103
4
votes
1
answer
97
views
What does Dash Question mark do? [closed]
This is an example I'm reading that picks out the Primes, but I don't quite see how the _? works. I haven't seen it before and can't find it in Help.
...
- 599
5
votes
1
answer
395
views
I understand b_ matches beta, but why does it also match alpha?
Why does this pick out everything instead of just beta?
Cases[{alpha, beta, mxyzptlk}, b_]
In a function you have to match the ...
- 599
0
votes
0
answers
104
views
Removing "spikes" in data
Imagine I have a data set which gives me the following ListLinePlot
Is it possible to define a function over the data set that removes the "spikes" ...
- 4,187
2
votes
3
answers
116
views
1
vote
1
answer
97
views
How to use Fold on Select with a list of conditions to progressively eliminate from a list?
The application of Reduce (over the integers) to an equation produces, after the application of LogicalExpand, a list of 1296 And'ed logical conditions (in 9 generated parameters, 5 of which are ...
- 2,560
0
votes
1
answer
52
views
0
votes
0
answers
94
views
Motion blurring in the frequency domain
My task is to implement a motion blurring filter via the frequency domain. The transfer function for this is as follows:
I previously consulted this answer for starter code. My function is shown below:...
- 1
4
votes
6
answers
438
views
How to leave only rows satisfying a particular condition from a table?
Consider the following table:
tab={{1,2},{3,67},{96,1},{1,19},{894,55},{10111,23},{20000,23},{5,93},{5,97},{22,34},{0,1}};
How to select only those rows for which <...
- 4,984
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votes
1
answer
64
views
1
vote
3
answers
100
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2
votes
2
answers
102
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