New answers tagged filtering
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How to select elements from a list of pairs based on first element belonging to a different list?
Using Cases, FreeQ and Condition:
...
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How to select elements from a list of pairs based on first element belonging to a different list?
Here we can use <| |>
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1
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How to select elements from a list of pairs based on first element belonging to a different list?
Position[listA[[All,1]], Alternatives@@listB]//Extract[listA,#]&
(* {{1, a}, {3, c}, {5, e}} *)
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2
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How to select elements from a list of pairs based on first element belonging to a different list?
One of many ways
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2
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Accepted
How to select elements from a list of pairs based on first element belonging to a different list?
Here is one way to do it:
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3
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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
PowerModList[-1, 1/4, 17]
{2, 8, 9, 15}
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2
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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
Solve[x^4 == -1, Modulus -> 17]
(* {{x -> 2}, {x -> 8}, {x -> 9}, {x -> 15}} *)
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2
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Accepted
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
Select[Range[16],
Function[x,Mod[x^4+1,17]==0]]
(* {2,8,9,15} *)
Alternative syntax:
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5
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What does Dash Question mark do?
This is called conditional pattern-matching.
From Professor Richard J. Gaylord's Wolfram Language Fundamentals Part One at time 57:04
See also using-a-patterntest-versus-a-condition-for-pattern-...
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10
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I understand b_ matches beta, but why does it also match alpha?
You've severely misunderstood how pattern matching of Mathematica works. _ is not wildcard character like ? or ...
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