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Re: Efficient search for bounding list elements

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  • Subject: [mg114192] Re: Efficient search for bounding list elements
  • From: Alexei Boulbitch <alexei.boulbitch at>
  • Date: Fri, 26 Nov 2010 05:31:01 -0500 (EST)

Hi, David,


searchFunction[x_, a_] := {Last@Select[a, #<  x&],
    First@Select[a, #>  x&]}

may give the answer you are looking for.
Let us try:
a = Range[1000, 5000, 250];
x = 1800;
searchFunction[x, a]

{1750, 2000}

Have fun, Alexei

I've been looking for a way to efficiently find the indices of the two
elements of a monotonically increasing list which bound a number.  For
example, if

a = Range[1000,5000,250]



then I'd like this function (e.g., searchFunction[x,a]) to return
{3,4}, which correspond to the 3rd and 4th elements of a, which are
1500 and 1750, respectively.

I can easily do this in a loop, but in my application a can be very
large (hundreds of thousands or millions of elements) and this
operation needs to repeated thousands of times, so efficiency is

Any suggestions would be greatly appreciated!


David Skulsky

Alexei Boulbitch, Dr. habil.
Senior Scientist
Material Development

ZAE Weiergewan
11, rue Edmond Reuter

Tel: +352 2454 2566
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