memory-efficient | 易学教程

Efficiency of flattening and collecting slices

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问题 If one uses the standard .flatten().collect::<Box<[T]>>() on an Iterator<Item=&[T]> where T: Copy , does it: perform a single allocation; and use memcpy to copy each item to the destination or does it do something less efficient? 回答1: Box<[T]> does not implement FromIterator<&T> , so I'll assume your actual inner iterator is something that yields owned T s. FromIterator<T> for Box<[T]> forwards to Vec<T> , which uses size_hint() to reserve space for lower + 1 items, and reallocates as it

Is the wide or long format data more efficient?

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问题 I am just curious whether it is more efficient to store data in long or wide format regardless of the interpretative? I have used object.size() to determine the size in the memory but they do not differ significantly (the long being slightly more efficient in terms of size) and the value is only and estimate. On top of the raw size, I am also wondering which of the format is more efficient in terms of being manipulated when used in modelling. 回答1: The memory usage of the two different matrix

Memory efficient multivaluemap

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Hi I have the following problem: I'm storing strings and a corresponding list of integer values in an MultiValueMap<String, Integer> I'm storing about 13 000 000 million strings and one string can have up to 500 or more values. For every single value i will have random access on the Map. So worst case are 13 000 000* 500 put calls. Now the speed of the map is good but the memory overhead gets quite high. A MultiValueMap<String, Integer> is nothing else then a HashMap/TreeMap<String, <ArrayList<Integer>> . Both HashMap and TreeMap have quite a lot of memory Overhead. I wont be modifying the map

Is there a way to paste together the elements of a vector in R without using a loop?

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Say there's a vector x: x <- c("a", " ", "b") and I want to quickly turn this into a single string "a b". Is there a way to do this without a loop? I know with a loop I could do this: y <- "" for (i in 1:3){ paste(y, x[i], sep = "") } > y [1] "a b" but I will need to do this over many, many iterations, and having to loop over this and replace the original with the new each time would become very time consuming. I always want to be able to do something like this: x <- paste(x) as if paste() could smartly divide up the elements of a vector itself, but I know it can't. Is there another function,

How do you design FIFO queue with variable data size?

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问题 I'm just working on the FIFO queue (the simple one, just what's pushed first, pops at first) with the variable data size but I'm not sure with the way I'm designing it. The data types I will store there will be known in advance and let's say will be the same for each instance of this class. I was thinking about using TList where the records with the following definition will be stored (@David - it's for D2007, so I have no Generics.Collections available :) type PListItem = ^TListItem;

Efficient ListView in android

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What is the best way of constructing a ListView that uses the least memory possible? This is important, because I met a few implementations and most of them is lagging when I scroll the ListView on low-end devices, but I saw a few apps, where the scroll is very smooth, even on low-end devices. How can it be done? What is the most efficient way from a memory usage point of view to construct such a ListView ? recycle your views in getView() use ViewHolder pattern use lazy loading if you have a lot of data to fill the list with use Cursor as underlying data instead of object list built from

Split a 3D numpy array into 3D blocks

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问题 I would like to split a 3D numpy array into 3D blocks in a 'pythonic' way. I am working with image sequences that are somewhat large arrays (1000X1200X1600), so I need to split them into pieces to do my processing. I have written functions to do this, but I am wondering if there is a native numpy way to accomplish this - numpy.split does not seem to do what I want for 3D arrays (but perhaps I don't understand its functionality) To be clear: the code below accomplishes my task, but I am

Need help in developing DB logic

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This is a mini-project of mine - Airline reservation system - lets call this airline FlyMi : I have a database (Not decided which one, friend of mine wants to go with MongoDB). Anyhoo, this is my requirement : I have a table which has details of the flight - Flight number, schedule etc. I'm going to use this table to perform various operations - booking , cancellation , modification This is where I'm stuck : For the desktop app and the web application - I'm offering an option to select seats. This means I've got to keep track of which seats are booked , which ones are not. And assume I have an

More efficient query to avoid OutOfMemoryError in Hive

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问题 I'm getting a java.lang.OutOfMemoryError: GC overhead limit exceeded in Hive. In searching I've found that is because 98% of all CPU time of the process is going to garbage collect (whatever that means?). Is the core of my issue in my query? Should I be writing the below in a different way to avoid this kind of problem? I'm trying to count how many of a certain phone type have an active 'Use' in a given time period. Is there a way to do this logic differently, that would run better? select

Efficient ListView in android

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问题 What is the best way of constructing a ListView that uses the least memory possible? This is important, because I met a few implementations and most of them is lagging when I scroll the ListView on low-end devices, but I saw a few apps, where the scroll is very smooth, even on low-end devices. How can it be done? What is the most efficient way from a memory usage point of view to construct such a ListView ? 回答1: recycle your views in getView() use ViewHolder pattern use lazy loading if you