Python list deduplication, Python list
Boring statistics on how many methods are available to deduplicate the list.
1. Set
list(set(alist))
To maintain the order:
import randomif __name__=='__main__': a=[random.randint(0,10) for i in xrange(10)] b=list(set(a)) b.sort(key=a.index)
2. Dictionary
Most of them use the hash table feature
{}.fromkeys(alist).keys()
Or manually write:
import randomif __name__=='__main__': a=[random.randint(0,10) f
Example of deduplication of php Arrays
This article mainly introduces the example of de-duplicated data in php arrays. Sometimes the obtained php arrays always contain duplicate values. You can use the following method to remove duplicate data.
Repeated data starting with a number is as follows:
The Code is as follows:
Array (
[0] = gt; 100
[K1] = gt; 100
[1] => 2123.
[K2] = gt; 2123)
This method can remove the value of the number as
Js deduplication and js merge
1. deduplicationFor (var q = 0; q } If (! IsExist) {s. push (matchCode) ;}} 3. group var map ={}, dest = []; for (var I = 0; I
Array deduplication is difficult to calculate. there is an array that needs to be deduplicated. the format of the array is discussed online.
Reply to discussion (solution)
Paste the sample array output by var_export. the basis for not discussing is not discussed. In fact, it is very simple. you only need to press the cluster key to cluster.
Paste the sample array output by var_export. the basis for not discussing is not discussed. In fact, it
1. Save All accessed URLs in the database2. Save the accessed URL in the memory and query the URL at the O (1) cost.1000000000 * 2byte * 50 characters/1024/1024/1024 ≈ 9G3. the URL is hashed by MD5 and then saved to the memory (the method used by scrapy)4. Use the bitmap method to map the accessed URL to a certain location using the hash function.5. The bloomfilter method improves bitmap and multiple hash functions reduce conflicts.Crawler deduplication
");3. Test situationTest methodFirst time (unit ms)First time (unit ms)15214ms5735ms2299ms290Ms359ms28ms426ms26msIii. Conclusion1, using ExecuteSQL delete the fastest, the database is the most efficient.2, Deletesearchedrows and ExecuteSQL belong to bulk Delete, better performance.3, the query results deleted, the slowest, if you use this method, set up you immediately modify your program, because you are wasting time.4.The number of small data records is less than 500,000, use deletesearchedrow
In the table, duplicate values may be included. That's not a problem, but sometimes you might want to just list different values (distinct). Keyword DISTINCT is used to return only different values.Table A:Example 1Select distinct name from AThe following results are performed:Example 2Select DISTINCT name, ID from AThe following results are performed:is actually based on "Name+id".Example 3: StatisticsSelect COUNT (distinct name) from A; --The number of the table name to go back to, SQL Server
Php array deduplication and analysis. Duplicate items in one-dimensional array: Use the array_unique function. use the following example: Copy the code as follows :? Php $ aaarray (apple, banana, pear, apple, wail, watermalon); $
Repeated items in one-dimensional array:
Use the array_unique function. use the following example:
The code is as follows:
$ Aa = array ("apple", "banana", "pear", "apple", "wail", "watermalon ");$ Bb = array_unique ($ a
directory.
Result indicates the entire record. File obtains the final output file name, hash, bitwise operation, and modulo operation for output balancing.
Map output structure The purpose of this operation is to ensure that the same record has the same key and save the type. Partition needs to press left of textpair, that is, this key,
This ensures that all records to be written to the same output file are written to the same reduce. One reduce can write multiple output files, but one output f
Note:
It tells you that N numbers allow you to keep one repeated number and sort the output.
Analysis:
Store a number every time it is read.
There were countless RESS yesterday because I first output the first one and then output each one in sequence.
The problem is that if only one element needs to access the first element
Code:
1 #include View code
1 #include Array Simulation
Hlg1287 number deduplication and sorting II [hash]
(*) from gczbxx_zhao t group by gcmc, gkrq having
Count (*)> = 1 order by GKRQ)
Select * from gczbxx_zhao where viewid in (select max (viewid) from gczbxx_zhao group
Gcmc) order by gkrq desc --- this is feasible.
.One question says: the efficiency of distinct deduplication is very low. I saw this article on the Internet as if it was very efficient to use group by having?In a test, I have a product table with 0.26 million records. Only the product num
ZOJ question 2734 Exchange Cards (DFS deduplication OR primary function)
Exchange Cards
Time Limit: 2 Seconds Memory Limit: 65536 KB
As a basketball fan, Mike is also fond of collecting basketball player cards. but as a student, he can not always get the money to buy new cards, so sometimes he will exchange with his friends for cards he likes. of course, different cards have different value, and Mike must use cards he owns to get the new one
004 string deduplication (keep it up), 004 keep
Design algorithms and write code to remove repeated characters in strings. No extra cache space is available. Note: one or two additional variables can be used, but an additional array copy is not allowed.
Simple question:
#include
Keep it up writes several algorithm questions every week, entertainment!
What is keep it up?
Keep upPersistence; maintenance; continue; Do not low; do not bend (disease, et
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