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Questions tagged [lookup]

Look up is related to indexes and hash tables. It is the action of accessing fastly to an item in a large collection thanks to a index (a so-called lookup table).

In computer science, a lookup table is an array that replaces runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an 'expensive' computation or input/output operation.

The tables may be precalculated and stored in static program storage, calculated (or "pre-fetched") as part of a program's initialization phase (memoization), or even stored in hardware in application-specific platforms. Lookup tables are also used extensively to validate input values by matching against a list of valid (or invalid) items in an array and, in some programming languages, may include pointer functions (or offsets to labels) to process the matching input.

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Fastest way to find an item in a list?

I have an unsorted list of strings. I can place these items in an array, List, SortedList, whatever. I need to find the fastest way of looking up a string in this list. Am I better off dumping the list into an array, sorting it, then implementing…
AngryHacker
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Reverse DNS lookup in perl

How do I perform a reverse DNS lookup, that is how do I resolve an IP address to its DNS hostname in Perl?
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What is the proper way to track indexes in python?

Right now I am tracking my index in side the loop like this index = 0 for entry in longList: if entry == 'foo': print index index += 1 is there a better way to do this?
John
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Find-or-insert with only one lookup in C# Dictionary

I'm a former C++/STL programmer trying to code a fast marching algorithm using C#/.NET technology... I'm searching for an equivalent of STL method map::insert that insert a value at given key if not exists, else returns an iterator to the existing…
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When should I raise LookupError in python?

Python's built-in exception documentation defines LookupError as: The base class for the exceptions that are raised when a key or index used on a mapping or sequence is invalid: IndexError, KeyError. This can be raised directly by…
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How to lookup only for specific fields in mongo

How to join only specific fields? When using $lookup, mongo returns the whole document. Let's say that's my data: users [ { id: 0, name: "Bob", adj: 1 }, { id: 1, name: "Will", adj: 2 }, ] adjectives [ { id: 1, name: "awesome" }, {…
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Get value from dictionary for first key that exists

TL;DR Is there a Python dictionary method or simple expression that returns a value for the first key (from a list of possible keys) that exists in a dictionary? Details Lets say I have a Python dictionary with a number of key-value pairs. The…
Andrew Guy
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Checking if Date is Between two Dates in R

I have two large datasets, df1 and df2. The first dataset, df1, contains the columns 'ID' and 'actual.data'. df1 <- data.frame(ID=c(1,1,1,2,3,4,4),…
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Making a grid-like data type in haskell

Problem I've been wondering how this could be done efficiently for a while, but for some reason I have been unable to do it. I need to model a rectangular grid, where each field contains some data. I need to access it via a zipper, where my focus is…
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Many to many lookups in Django

This is probably insultingly simple and worthy of a Nelson Muntz laugh, but I'm having a real braindead moment tryng to make many to many connections across various model relationships. I have the following models (simplified for your…
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Converting Lookup into other data structures c#

I have a Lookup where the TElement refers to a string of words. I want to convert Lookup into: Dictionary or List> ? I have read some articles about using the Lookup but it…
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$aggregation and $look up in the same collection- mongodb

The structure is more or less like; [ {id: 1, name: "alex" , children: [2, 4, 5]}, {id: 2, name: "felix", children: []}, {id: 3, name: "kelly", children: []}, {id: 4, name: "hannah", children: []}, {id: 5, name: "sonny",…
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is locking necessary for Dictionary lookup?

lock(dictionaryX) { dictionaryX.TryGetValue(key, out value); } is locking necessary while doing lookups to a Dictionary ? THe program is multithreaded, and while adding key/value to dict. dict is being locked.
DarthVader
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Mongodb - regex match of keys for subdocuments

I have some documents saved in a collection (called urls) that look like this: { payload:{ url_google.com:{ url:'google.com', text:'search' } } }, { payload:{ url_t.co:{ …
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Is there a publicly available list of the US States in machine readable form?

Where can I find a list of the US States in a form for importing into my database? SQL would be ideal, otherwise CSV or some other flat file format is fine. Edit: Complete with the two letter state codes
user59861
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