[R] More simple implementation is slow.

[wl2776]

Sorry, here are the profiles:

summaryRprof("get_tau")
$by.self
         self.time self.pct total.time total.pct
"cbind"       0.02       50       0.04       100
"unlist"      0.02       50       0.02        50

$by.total
          total.time total.pct self.time self.pct
"cbind"         0.04       100      0.02       50
"get_tau"       0.04       100      0.00        0
"unlist"        0.02        50      0.02       50
"apply"         0.02        50      0.00        0

$sample.interval
[1] 0.02

$sampling.time
[1] 0.04

summaryRprof("get_tau2")
$by.self
         self.time self.pct total.time total.pct
"FUN"         0.48    51.06       0.84     89.36
"$"           0.34    36.17       0.34     36.17
"ls"          0.08     8.51       0.08      8.51
"+"           0.02     2.13       0.02      2.13
"lapply"      0.02     2.13       0.02      2.13

$by.total
                    total.time total.pct self.time self.pct
"apply"                   0.86     91.49      0.00     0.00
"get_tau2"                0.86     91.49      0.00     0.00
"FUN"                     0.84     89.36      0.48    51.06
"$"                       0.34     36.17      0.34    36.17
"ls"                      0.08      8.51      0.08     8.51
"apropos"                 0.08      8.51      0.00     0.00
".completeToken"          0.08      8.51      0.00     0.00
"normalCompletions"       0.08      8.51      0.00     0.00
"+"                       0.02      2.13      0.02     2.13
"lapply"                  0.02      2.13      0.02     2.13
"unlist"                  0.02      2.13      0.00     0.00

$sample.interval
[1] 0.02

$sampling.time
[1] 0.94

I also was advised to use 
    with(cpt, sqrt(outer(x, x, "-")^2 + outer(y, y, "-")^2) )

And here is its profile 
summaryRprof("with")
$by.self
       self.time self.pct total.time total.pct
"gsub"      0.02      100       0.02       100

$by.total
                     total.time total.pct self.time self.pct
"gsub"                     0.02       100      0.02      100
".completeToken"           0.02       100      0.00        0
"grep"                     0.02       100      0.00        0
"keywordCompletions"       0.02       100      0.00        0
"makeRegexpSafe"           0.02       100      0.00        0
"normalCompletions"        0.02       100      0.00        0
"sprintf"                  0.02       100      0.00        0

$sample.interval
[1] 0.02

$sampling.time
[1] 0.02

Apparently, it is about twise faster.

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