按照原样使用您的方法,您可以更改一些内容以提高效率。
1)nchar
是一个函数,它不像length
必须计算其参数的字符数,而不是获得属性。您将为每个“v1”的“v2”计算nchar
,但对于每个“v2”的“v1”,还要计算nchar
。您可以将nchar(x)
放在第二个sapply
之外,或者甚至更好地利用nchar
的向量化特性,并计算所有内容,并在任何sapply
之前计算所有内容。特别地,具有
x = replicate(1e3, paste0(sample(letters, sample(4:10, 1), TRUE), collapse = ""))
y = replicate(1e3, paste0(sample(letters, sample(4:10, 1), TRUE), collapse = ""))
代替
system.time({
nx = nchar(x)
ny = nchar(y)
})
#user system elapsed
# 0 0 0
使用
system.time({
sapply(x, function(X)
sapply(y, function(Y) {
nX = nchar(X)
nY = nchar(Y)
}))
})
#user system elapsed
#8.08 0.00 8.27
2)substring
被矢量化,所以能够避免第三sapply
。 (另外,在检查的字符串的单个字符,strsplit
可能更快,并且本身被矢量化,可以在任何循环之外进行计算。)
3)的if else
块比较“长度时比ifelse
更快== 1'载体。这完全是次要的,当然,但后两个嵌套sapply
的IT增加了额外的计算时间,而无需:
microbenchmark::microbenchmark(replicate(1e4, if(2 < 3 && 5 > 3) 1 else 0),
replicate(1e4, ifelse(2 < 3 && 5 > 3, 1, 0)))
#Unit: milliseconds
# expr min lq median uq max neval
# replicate(10000, if (2 < 3 && 5 > 3) 1 else 0) 14.22543 14.85759 15.09545 15.78781 56.84884 100
# replicate(10000, ifelse(2 < 3 && 5 > 3, 1, 0)) 29.77642 31.44824 36.20305 37.85782 65.72473 100
因此,考虑到有这些:
OP2 = function(v1, v2)
{
nc1 = nchar(v1)
nc2 = nchar(v2)
sv2 = seq_along(v2)
sapply(seq_along(v1),
function(i) {
sapply(sv2,
function(j) {
len = if(nc1[[i]] > nc2[[j]]) nc1[[i]] else nc2[[j]]
ind = seq_len(len)
sum(substring(v1[[i]], 1, ind) == substring(v2[[j]], 1, ind))/len
})
})
}
并与你的比较:
set.seed(007)
v1b = replicate(1e2, paste0(sample(letters[1:5], sample(4:10, 1), TRUE), collapse = ""))
v2b = replicate(1e2, paste0(sample(letters[1:5], sample(4:10, 1), TRUE), collapse = ""))
sum(count.first.character.matches(v1b, v2b) != OP2(v1b, v2b))
#[1] 0
microbenchmark::microbenchmark(count.first.character.matches(v1b, v2b), OP2(v1b, v2b), times = 20)
#Unit: milliseconds
expr min lq median uq max neval
# count.first.character.matches(v1b, v2b) 932.2840 949.3697 969.6321 985.2237 1081.2882 20
# OP2(v1b, v2b) 161.7503 185.1102 192.3019 197.5060 213.6818 20
另一个想法,除了你的方法,可能是(改变“OP2”,以保持最短的长度后):
ff = function(x, y)
{
sx = strsplit(x, "", fixed = TRUE)
sy = strsplit(y, "", fixed = TRUE)
array(mapply(function(X, Y) {
slen = seq_len(min(length(X), length(Y)))
wh = X[slen] == Y[slen]
if(all(wh)) return(1) else (which.min(wh) - 1)/length(slen)
},
rep(sx, each = length(sy)), sy),
c(length(x), length(y)), list(y, x))
}
sum(ff(v1b, v2b) != OP2(v1b, v2b))
#[1] 0
microbenchmark::microbenchmark(ff(v1b, v2b), OP2(v1b, v2b), times = 20)
#Unit: milliseconds
# expr min lq median uq max neval
# ff(v1b, v2b) 72.72661 80.43703 85.85113 89.16066 110.5722 20
# OP2(v1b, v2b) 165.13991 168.15051 176.01596 182.11389 213.9557 20
看看'stringdist'包 –
你的'short_length'应该设置为'ifelse(nx