Lua中的LZW压缩 [英] LZW Compression In Lua
问题描述
这是 Lempel-Ziv-Welch 压缩的伪代码.
Here is the Pseudocode for Lempel-Ziv-Welch Compression.
pattern = get input character
while ( not end-of-file ) {
K = get input character
if ( <<pattern, K>> is NOT in
the string table ){
output the code for pattern
add <<pattern, K>> to the string table
pattern = K
}
else { pattern = <<pattern, K>> }
}
output the code for pattern
output EOF_CODE
我正在尝试在 Lua 中对此进行编码,但它并没有真正起作用.这是我在 Python 中的 LZW 函数之后建模的代码,但我在第 8 行收到尝试调用字符串值"错误.
I am trying to code this in Lua, but it is not really working. Here is the code I modeled after an LZW function in Python, but I am getting an "attempt to call a string value" error on line 8.
function compress(uncompressed)
local dict_size = 256
local dictionary = {}
w = ""
result = {}
for c in uncompressed do
-- while c is in the function compress
local wc = w + c
if dictionary[wc] == true then
w = wc
else
dictionary[w] = ""
-- Add wc to the dictionary.
dictionary[wc] = dict_size
dict_size = dict_size + 1
w = c
end
-- Output the code for w.
if w then
dictionary[w] = ""
end
end
return dictionary
end
compressed = compress('TOBEORNOTTOBEORTOBEORNOT')
print (compressed)
我真的很想得到一些帮助,要么让我的代码运行,要么帮助我在 Lua 中编写 LZW 压缩.非常感谢!
I would really like some help either getting my code to run, or helping me code the LZW compression in Lua. Thank you so much!
推荐答案
假设 uncompressed
是一个字符串,你需要使用这样的东西来迭代它:
Assuming uncompressed
is a string, you'll need to use something like this to iterate over it:
for i = 1, #uncompressed do
local c = string.sub(uncompressed, i, i)
-- etc
end
第 10 行还有一个问题;..
在 Lua 中用于字符串连接,所以这一行应该是 local wc = w .. c
.
There's another issue on line 10; ..
is used for string concatenation in Lua, so this line should be local wc = w .. c
.
关于字符串连接的性能,您可能还想阅读this.长话短说,将每个元素保存在表中并使用 table.concat()
返回它通常更有效.
You may also want to read this with regard to the performance of string concatenation. Long story short, it's often more efficient to keep each element in a table and return it with table.concat()
.
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