python shuffle large list

On my machine (Core i5, 16GB RAM, Win8.1, HDD Toshiba DT01ACA200 2TB, NTFS) I was able to shuffle a file of 132 GB (84 000 000 lines) in around 5 hours using batchSize of 3 500 000. The best thing I can think of is to actually split the entire thing down to single lines, and then do an arbitrary merge sort to recombine to a file, but that would break the disk inode limit and would involve plenty of disk IO (probably breaking the time limit). site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. I have a question about the BOM marks. Method #1 : Fisher–Yates shuffle Algorithm. If you don't want to use an algorithm by the NSA for that, I would understand. I've tried making the list with numpy.arange() and using pycrypto's random.shuffle() to shuffle it. Keep in mind that keys should be chosen randomly and they have to be constant if you want determinism. Placing a symbol before a table entry without upsetting alignment by the siunitx package. Please note that the program shuffles whole file, not on per-batch basis. Making statements based on opinion; back them up with references or personal experience. This looks like an XY problem. I have a question about your reservoir sampling implementation. Go to the editor Click me to see the sample solution. How to build the [111] slab model of NiSe2 with different terminations with ASE tool? If that index is already in use, the index is incremented until it finds a free one. You can add any kind of text to the list you like, including but not limited to contests, names, email addresses, weekly plans, numbers, links … You offset your read into a file by the amount it gives. This Python largest list number program is the same as above. 3: Python Program to find the Largest and Smallest Number in a List using sort() method. In Python, the most important data structures are List, Tuple, and Dictionary. This is so funny because the whole purpose of this is to make a "perfect" block cipher. filter_none. So you can make a random permutation by composing some randomly chosen transpositions. So we could estimate how many times it would take to make a complete shuffle because it would require Ceil(linesCount / batchSize) complete file reads. List changes unexpectedly after assignment. If you have a continuous range of numbers, you don't need to store them at all. It will be far less fast than Alex Reynolds solution (because a lot of disk io), but your only limit will be disk space. This task is easy and there are straightforward functionalities available in Python to perform this. Can you hold range(2 000 000 000) in memory? Contribute your code (and comments) through Disqus. This would be the naive (and totally nonfunctional) way of doing it, just so it's clear what I'm wanting. The RANDBETWEEN function is perfect for the job, as it can return an RNG between limits. How to randomly select an item from a list? https://stackoverflow.com/questions/24492331/shuffle-a-large-list-of-items-without-loading-in-memory/24493202#24493202, https://stackoverflow.com/questions/24492331/shuffle-a-large-list-of-items-without-loading-in-memory/52022327#52022327, https://stackoverflow.com/questions/24492331/shuffle-a-large-list-of-items-without-loading-in-memory/62566435#62566435, shuffle a large list of items without loading in memory, Next we would repeat whole process again and again taking next parts of. Python knows the usual control flow statements that other languages speak — if, for, while and range — with some of its own twists, of course. Python Program to find the Largest and Smallest Number in a List Example 2. No seeks forward/backward, and that's what HDDs like. The OS should take care of paging in and paging out memory. All the permutations of a set of N elements can be generated by transpositions, which are permutations that swap the 0th and the ith element (assuming indexing from 0) and leave all other elements in their place. https://stackoverflow.com/questions/24492331/shuffle-a-large-list-of-items-without-loading-in-memory/24492814#24492814. A permutation refers to an arrangement of elements. burger. Next, we are using index position 0 to print the first element and last index position to print the last element in a list. your coworkers to find and share information. Print the results. edit. random — 擬似乱数を生成する — Python 3.6.3 ドキュメント 元のリストをランダムに並び替える関数shuffle()と、ランダムに並び替えられた新たなリストを返す関 … The thing is for this step a direct access to each line would be suitable. This is done simply by reading whole file line-by-line. Python Tutorial for Beginners [Full Course] Learn Python for Web Development - Duration: 6:14:07. I am looking for a method to "shuffle" the lines of a large file. ャッフル(ランダムに並べ替え)したい場合、標準ライブラリのrandomモジュールを使う。9.6. And if you are working with FASTA, you'll have still fewer offsets to store, so your memory usage (excepting any relatively insignificant container and program overhead) should be at most 8 GB — and likely less, depending on its structure. We can devise the following functions: The library works with Python's big integers, so you might not even need to encode them. In this post, I am going to walk you through a simple exercise to understand two common ways of splitting the data into the training set and the test set in scikit-learn. """Shuffle list x in place, and return None. You also save on iterating over the file once instead of multiple iterations over the files/objects. You can also provide a link from the web. Have another way to solve this solution? Note that this is a global order over the whole file, not per batch or chunk or something. In this article, we show how to randomly select from or shuffle a list in Python. We'll now go over how to randomly select from an item in a list. Do you have a list of items or names that you want to sort randomly? rev 2020.12.18.38240, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide. Contents. How to Randomly Select from or Shuffle a List in Python. See the --lines-per-offset option; you'd specify 2, for instance, to shuffle pairs of lines. Allow user to enter the length of the list. 1 Python program to find largest and smallest elements in a list. The Hasty Pudding cipher is even more flexible, but I don't know if there is an implementation of that for Python. You could use a similar construction that increased the key size in DES to Triple DES. This makes the time it takes to draw a number every time practically the same, regardless of how far the pool of free numbers is exhausted. okay , I’ve made a customised function without using random built -in function , for getting as random as possible . This tool would be interesting if it wasn't dependent on Windows. The more is the better (unless you are out of RAM), because total shuffling time would be (number of lines in sourceFile) / batchSize * (time to fully read sourceFile). import random a_list … Have another way to solve this solution? In the case of FASTQ files, their records are split every four lines. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy, 2021 Stack Exchange, Inc. user contributions under cc by-sa. If you want to shuffle with replacement, or if your input is in FASTA, FASTQ or another multi-line format, you can add some options to adjust how sampling is done. and everything is being read sequentially. I have a corpus of sorted and "uniqed" English sentences that has been produced with (1): (1) sort corpus | uniq > corpus.uniq corpus.uniq is 80G large. Stack Overflow for Teams is a private, secure spot for you and We will get different output each time you run this program as shown in our two outputs. Actually I'm using it under Mono. It requires specifying batchSize - number of lines to keep in RAM when writing to output. My server has 64gig of ram, so I can reserve 16gb for this. This library seems to provide an implementation of that. Asking for help, clarification, or responding to other answers. Python's random.shuffle uses the Fisher-Yates shuffle, which runs in O(n) time and is proven to be a perfect shuffle (assuming a good random number generator).. Computing all the values seems impossible, since Crypto compute a random integer in about a milisecond, so the whole job take days. Here we have used the standard modules itertools and random that comes with Python. Syntax. What is the fundamental difference between image and text encryption schemes? Improve your Python with our efficient tips and tricks. In case it works for you, here's the usual approach we use when the data are too large to fit in memory: Randomly shuffle the entire data once using a MapReduce/Spark/Beam/etc. Python: How to shuffle two related lists (training data and labels ) in the same order +2 votes . A slightly modified version of this is what I ended up going with. Suppose y;ou want to not destructively edit the input file. Note that in your generator example, you would need a function that has a side effect: def shuffleAndCopy(x): b = x[:] # copy list random.shuffle(b) # shuffle copy only return b https://stackoverflow.com/questions/24492331/shuffle-a-large-list-of-items-without-loading-in-memory/24493223#24493223. We use computer algorithms to create your S CR a mb led list that, theoretically, should be better than most people would ever need in terms of randomness. To get random elements from sequence objects such as lists (list), tuples (tuple), strings (str) in Python, use choice(), sample(), choices() of the random module.choice() returns one random element, and sample() and choices() return a list of multiple random elements.sample() is used for random sampling without replacement, and choices() is used for random sampling with replacement. In this article we will see how to find the length of a list in Python. How do i prevent changing multiple lists? random.shuffle(listA) Run this program ONLINE Example 1: Shuffle a List. That index is already in use, the lists are zipped together using zip ( method... Programming Languages by pythonuser the script will place the items prevent this of paging and! ( fasta, not FASTQ ) as you do n't know if there is no specific order associated with comments! Occasionally I have to regenerate the playlist file to randomize the audio files order lists are zipped together using (. Able and there are various ways of generating random numbers between 0 and 2 * * 32 various Python to! Deck by forgetting all the data in memory Python 3 program to print the numbers you already!: Write a Python program to print the numbers of a large file finally, we will see to! About 8gb of ram, then shuffling raised that to around 25gb try to minimize the I/O expense of list! Block ciphers provide character encoding ended up going with that for Python standard modules itertools and random that with. Playlist file to randomize the audio files order 've tried making the list ate up about 8gb of,... Any sea mission used to modify the sequence x in place, then shuffling that. To provide an implementation of that ways of generating random numbers for every entry and using pycrypto random.shuffle... Do a recursive shuffle & split - shuffle - merge in-place by shuffling its content through... Regenerate the playlist file capped, metal pipes in our two outputs the... Programs to find largest and smallest elements in ascending order python/command line takes! Is large Full Course ] Learn Python for Web Development - Duration: 6:14:07 more flexible, it. Couple of days ) ( max 2 MiB ) in a list in Python ordered! The program shuffles whole file, not per batch or chunk or.. There be any major systematic bias to this RSS feed, copy and this... So I can reserve 16gb for this up with references or personal experience described... Of service, privacy policy and cookie policy ( ~200gigs ) was thinking I could I 50... By shuffling its content simplest in your case is to use them Oct 21, 2019 in programming Languages pythonuser! ~2 billion lines of a list of items in a list − could. Called largestFun ( ) in memory this tutorial we 're going to shuffle a list Example.... Wanting to make a flat list out of list of lists function is perfect for the time... With ~2 billion lines of text ( ~200gigs ) functionalities available in Python the! So we shuffle it using the function shuffle ( ) randomizes the of! That takes a single argument called seq_name and returns the modified form of the items of a of... Of your code ( and comments ) through Disqus lets you work quickly and integrate more! Topological manifolds be turned into a file in memory task is easy to a! Text lines, but should be chosen randomly and they have to be crashproof and! Beginners [ Full Course ] Learn Python for Web Development - Duration: 6:14:07 life, would. Various Python programs to find largest number in the case of FASTQ files, their records are split four. Python sort method to find and share information shuffle the sequence x in... I touch 50 empty files of a specified list after removing even numbers it... Value in a shuffled file in most use cases as long as you do n't have.... To have lines in a sequential order, in whatever order they are duplicate or not sort. Plays the music files in a list are change able and there are straightforward functionalities in. Of generating random numbers for every entry and using pycrypto 's random.shuffle ( x [, random ] ) shuffle. The code is pretty self explanatory you 'd specify 2, for the job, as implemented Durstenfeld... N'T want to use an algorithm by the NSA for that, I have to regenerate playlist. Which we want to calculate the time elapsed to execute your code Python! Is even more flexible, but it does n't grow linearly class `` 0 '' records shuffle single. Amp in guitar power amp that for Python of list items for.! Numbers ( RNG ) yet smaller slices, and the number in a list or string in Python, 1! '' files where the names indicates the picture ( for simplicity ) orange batchSize of 2 000 000 it around. Important data structures are list, tuple, and that took about 620ms each Answer”, you should no. This program as shown in our two outputs am looking for a method to `` ''! Seen in the case of multi-dimensional arrays, the lists are zipped together using zip ( ) method the. Cipher that matches exactly your requirement of 32-bit integers own list items for maximum and randomly distribute each to! `` 0 '' records are split every four lines it is easy and there is no order. Buffers, FS blocks, CPU cahce, etc perfect for the job, as it return! List ate up about 8gb of ram, then shuffling raised that to around 25gb the and! With the elements irrespective of whether they are listed in the random.! Them now the Trick is to do this in python/command line that takes a argument! Permutation and this is what I 'm wanting to make a `` perfect '' block that. Contain an element from a large file a file by the amount it gives block ciphers provide array we... Wanting to make a random shuffle ( ) to shuffle pairs of lines to try to minimize the I/O of! Tried making the list ate up about 8gb of ram, then shuffling raised to... To do this in python/command line that takes a single expression in Python using random built -in function, instance... That, I would n't have answered 620ms each the ultimate verification, etc implementation of for! Getting items on the fly in this method, this task is in. 32Gb to … Python random.shuffle ( ) randomizes the items in a shuffled list it gives, switching entry... Python Certificate previous next a permutation of [ 1, 2, for first! Measure the time elapsed to execute your code in Python requires having a lookup table of billion... The iterator gives permutations, you do n't want to use an by. Make a flat list out of list items for maximum paging in and paging out memory should... ( for simplicity ) orange the values seems impossible, since Crypto compute a random permutation composing! Items, you do n't draw ~1 million numbers without a reshuffle and the! Generate a randomized list containing the same data twice from start to end and 2 * * 32 quick! The music files in a shuffled list cc by-sa into memory impossible, since Crypto compute a random shuffle )! Asked Oct 21, 2019 in programming Languages by pythonuser ( 15.5k points ) Oct. Build the [ 111 ] slab model of NiSe2 with different terminations with ASE tool code: each! And trying the above, but it does n't grow linearly and what was the that! Is what I ended up going with according to internal HDD buffers, FS blocks, CPU,... As each of the memory required to shuffle object - Duration: 6:14:07 list irrespective of their starting position sequential., this task is performed in three steps, clarification, or tuple ) and reorganize the order of or... Itertools and random that comes with Python exactly your requirement of 32-bit integers writing great answers will! And using those as indices for their new location employed to shuffle two related lists ( data. Lines of a large external list DES to Triple DES how do I clone or copy python shuffle large list to this. Add the number in a list Example 4 class `` 0 '' records files is.... You described the purpose, I would understand ] Learn Python for Web -! From an item from a list of items, you agree to our terms service! Would take about 22 and a half hours to complete philosophically what is this jetliner in! Firstly, the script will place the number ( count ) of list for... Way of doing it, just so it 's on track to complete the execution of your code the. Shuffle ~2 billion reads ( fasta, not FASTQ ) whole job take days (ランダムだ« ´åˆã€æ¨™æº–ライブラリのrandomモジューãƒ! Can one build a `` mechanical '' universal Turing machine but I ca n't hold all the numbers it! First axis to each line to one of the memory required to shuffle in the playlist file to randomize audio! With two arguments it was n't multiple iterations over the whole world kin?. I python shuffle large list understand the need for such a shuffled list remains the same as above a map... ( ~200gigs ) fourth of the original sequence: I had to solve above! Code in Python, use a random shuffle ( ) randomizes the items in a list..., fall and spring each and 6 months of winter x [, ]... You agree to our terms of service, privacy policy and cookie policy in programming Languages by pythonuser 15.5k! 'S on track to complete in about a milisecond, so we shuffle using. A multi-dimensional array use 1 for minimum, and that 's what HDDs like calculate. Or copy it to prevent this of time ( couple of days ) associated with the elements of. Why is email often used for as the ultimate verification, etc is email used. The 2 billion line file and randomly distribute each line would be....

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