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- #Lua table insert sorted inmemory hashmap how to#
- #Lua table insert sorted inmemory hashmap code#
- #Lua table insert sorted inmemory hashmap plus#
- #Lua table insert sorted inmemory hashmap professional#
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#Lua table insert sorted inmemory hashmap plus#
Function ipairs() is iterated as while type(t) ~= ‘nil’ - not for all keys, but, on the plus side, in a predictable way, and the order is guaranteed.Table length operator #t is only defined for arrays without holes.Now let’s talk about the second half of the table - the array. OK, iteration for string keys is clear, no more questions. The cost of a search does not worsen when a dead node is present on the way to collision resolution. Task O(n) to search for it needs to be performed when deleting. Here’s the story: I developed a basic storage solution for a project using Java’s MappedByteBuffer class coupled with a RandomAccessFile and the Java NIO (New Input/Output) FileChannel. Generally, when the main node is deleted for the searched key, the link to the colliding element needs to be reassigned to the predecessor (if present) of this main node. With a Java heap size constrained to be very small (say, 16 MB) you can create an in-memory, off-heap data store that holds gigabytes of dataor even more. Collisions are resolved by the chain method. What is strongly discouraged is to add new keys to the table within the cycle as reallocation or re-hashing may occur, and then iteration will bust.Īn additional note from Igor Munkin: the reason is lookup in general, not iteration.
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This is done for a reason, to make it possible to delete values and not disturb iteration order.
#Lua table insert sorted inmemory hashmap code#
Conceptually, this is what the code looks like: The most complete version of code from the publication, including all the experiments, can be found on GitHub. This internal representation will affect behaviors of some functions, which I’m going to discuss here.įor demonstration, I took LuaJIT source code and patched the tostring() method a bit so that it would print out the size and all the contents of C structure to stdout using printf(). There’s something that is more important: two tables may contain the same keys and values, but differ in terms of internal representation. Moreover, as a Lua developer, I have no need to speculate about what a table looks like on the inside. I was about to describe the logic LuaJIT is guided by when new elements are inserted, but this a rather sophisticated algorithm. Both are represented by continuous storage areas. */Ī table has two parts: array and hashmap. Uint32_t hmask /* Hash part mask (size of hash part - 1). Uint32_t asize /* Size of array part (keys ). Scientifically speaking, a table is an associative array. Values of any type can be used as keys (except for nil). A table can be used both as a data array (if the keys are integer-valued) and as a key-value repository. Tables in Lua are the only composite data type designed to suit any purpose. There is another good presentation about tables in PUC-Rio implementation, if you’re interested. Our version is a bit patched as compared to the authentic LuaJIT, but the differences don’t impact tables. In this article, I’m going to discuss mostly LuaJIT 2.1.0, which is used in Tarantool. Lua has several implementations and several versions.
#Lua table insert sorted inmemory hashmap professional#
Lua is my primary professional programming language, and if one wants to write good code, one needs at least to peek behind the curtain. In this article, I’m going to tell you about the internals of Lua tables and special considerations for their use. I spent some time whittling it down to where I hope an example can show off all that can go wrong: \documentclass x-ray \& co to the end, pg.~2.I don’t know about you, but I really like to get inside all sorts of systems. I am completely puzzled about all sorts of weird errors that I am running into. I am trying to add keywords (with page numbers) to an in-memory array, and print a sorted sequential index at the end of my chapter.
#Lua table insert sorted inmemory hashmap how to#
Related to lualatex: how to add to string or table.