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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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JavaScript LHS and RHS Lookup

I was reading the Scopes and Closure of You don't know JS book by Kyle Simpson, specifically this topic Compiler Speak. There they mention the LHS and RHS lookup. I am failed to understand these two terms, can anyone help me to realize them?
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Which is faster to find an item in a hashtable or in a sorted list?

Which is faster to find an item in a hashtable or in a sorted list?
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Initializing Lookup

How do i declare a new lookup class for a property in the object initializer routine in c#? E.g. new Component() { ID = 1, Name = "MOBO", Category = new Lookup } The category bit always get a compile error. I have a property called…
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lookup function doesn't work with unsorted list

Why does this work, and looks up values correctly but once i change the order of values, it produces incorrect values?
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LINQ Convert Dictionary to Lookup

I have a variable of type Dictionary> I want to convert it to a Lookup. I wanted to use Lambda functions to first, flatten the dictionary and then convert this to Lookup using the ToLookup(). I got…
Anna
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What is the relationship between java:comp/env and java:global?

What is the relationship between java:comp/env and java:global (regarding 3.1 spec)? Seems like java:comp/env contains specific to EJB references. What means "specific" in this case?
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Create sine lookup table in C++

How can I rewrite the following pseudocode in C++? real array sine_table[-1000..1000] for x from -1000 to 1000 sine_table[x] := sine(pi * x / 1000) I need to create a sine_table lookup table.
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Dictionary data structure in R

In R, I have, for example: > foo <- list(a=1,b=2,c=3) If I type foo, I get: $a [1] 1 $b [1] 2 $c [1] 3 How can I look through foo to get a list of "keys" only? In this case, (a, b, c).
user187268
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Java HashSet equivalent in C++

I was curious if there was something akin the Java HashSet in C++? I.e. a data structure with a fast look, as I will only be running .contains(e) on it. Likewise, if you could enlighten me on how to do a .contains() on whatever data structure you…
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What is the best way to create a whois lookup?

I want add a domain registration in a website written with PHP. So I need a whois lookup service. What do I need to do? What's are its steps? Do I need a database, API or ... ? Help me please
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C# System.Linq.Lookup Class Removing and Adding values

I'm using Lookup class in C# as my prime data container for the user to select values from two Checked List boxes. The Lookup class is far easier to use than using the class Dictionary>, however I cannot find methods for removing and adding values…
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In R, What is the difference between df["x"] and df$x

Where can I find information on the differences between calling on a column within a data.frame via: df <- data.frame(x=1:20,y=letters[1:20],z=20:1) df$x df["x"] They both return the "same" results, but not necessarily in the same format. Another…
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Why is Lookup immutable in C#?

Unlike Dictionary, you cannot construct a Lookup by adding elements one by one. Do you happen to know the reason? Lookup is just like multimap in C++; why can't we modify it in C#? If we really can't, how can we construct a multimap data structure…
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How to convert string to objectId in LocalField for $lookup Mongodb

I want to add join collections using $lookup in mongodb. I am trying as below { $lookup:{ from:"User", localField:"assignedId", foreignField:"_id", as:"dataa"} } Now I have two collections User contains objectid of users like "_id"…
Saurabh Sharma
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How to check if an element exists in a Python array (Equivalent of PHP in_array)?

I'm new to Python and I'm looking for a standard function that would tell me if an element is present in an array. I found the index method but it throws an exception if the element is not found. I just need some simple function that would return…
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