arrays - R - avoid nested for loops -


i have following function takes 4 vectors. t vector has given length , 3 other vectors (pga, sa5hz , sa1hz) have given (identical not equal t) lenght.

the output matrix length(t) rows , length(pga) columns.

my code below seems perfect example of not do, however, not figure out way optimize using apply function. can help?

designspectrum <- function (t, pga, sa5hz, sa1hz){    ts <- sa1hz / sa5hz    #by convention, if sa5hz null, set ts 0.   ts[is.nan(ts)] <- 0    res <- matrix(na, nrow = length(t), ncol = length(pga))    (i in 1:nrow(res))   {     (j in 1:ncol(res))     {       res[i,j] <- if(t[i] <= 0) {pga[j]}                   else if (t[i] <= 0.2 * ts[j]) {pga[j] + t[i] * (sa5hz[j] - pga[j]) / (0.2 * ts[j])}                   else if (t[i] <= ts[j]) {sa5hz[j]}                   else sa1hz[j] / t[i]       }   }    return(res) }

instead of doing double for loop , processing each i , j value separately, use outer function process of them in 1 shot. since you're processing multiple i , j values simultaneously, switch vectorized ifelse statement instead of non-vectorized if , else statements:

designspectrum2 <- function (t, pga, sa5hz, sa1hz) {   ts <- sa1hz / sa5hz   ts[is.nan(ts)] <- 0   outer(1:length(t), 1:length(pga), function(i, j) {     ifelse(t[i] <= 0, pga[j],       ifelse(t[i] <= 0.2 * ts[j], pga[j] + t[i] * (sa5hz[j] - pga[j]) / (0.2 * ts[j]),         ifelse(t[i] <= ts[j], sa5hz[j], sa1hz[j] / t[i])))   }) } identical(designspectrum(t, pga, sa5hz, sa1hz), designspectrum2(t, pga, sa5hz, sa1hz)) # [1] true

data:

t <- -1:3 pga <- 1:3 sa5hz <- 2:4 sa1hz <- 3:5

you can see efficiency gains testing on rather large vectors (here i'll use output matrix 1 million entries):

# larger vectors set.seed(144) t2 <- runif(1000, -1, 3) pga2 <- runif(1000, -1, 3) sa5hz2 <- runif(1000, -1, 3) sa1hz2 <- runif(1000, -1, 3)  # runtime comparison all.equal(designspectrum(t2, pga2, sa5hz2, sa1hz2), designspectrum2(t2, pga2, sa5hz2, sa1hz2)) # [1] true system.time(designspectrum(t2, pga2, sa5hz2, sa1hz2)) #    user  system elapsed  #   4.038   1.011   5.042  system.time(designspectrum2(t2, pga2, sa5hz2, sa1hz2)) #    user  system elapsed  #   0.517   0.138   0.652

the approach outer 10x faster.


Comments

Post a Comment

Popular posts from this blog

html - Outlook 2010 Anchor (url/address/link) -

i'm trying link specific pdf page msoutlook'10 or msword'10, #page=... anchor particularly useful , works fine elsewhere. unfortunately when click [ctr-k] in outlook or winword, links re-formatted assuming unc path. pdf file located on shared drive. using "file:" prefix links open pdf in adobe reader (outside of browser), , "http:" open inside browser. issue seem need open in browser "file:" prefix in order anchor work. know anchors work inside browser. outlook uses windows/explorer default program (based on file extension) seems open in adobe reader neglecting anchor. is aware of solution, link specific page or bookmark of shared-pdf ms outlook and/or winword link? common references: mailermailer.com/...anchor-tags-html-emails campaignmonitor.com/...anchor-links-in-email-newsletters/ stackoverflow.com/...anchor-in-pdf-document
Read more

javascript - Why does running this loop 9 times take 100x longer than running it 8 times? -

consider code: test = function() { } t = new test(); (var = 0; < 8; i++) { result = t instanceof test; } if change number of iterations 8 9 , loop take 100 times longer complete in latest version of firefox (41.0.1). tested on 2 different pcs , magic limit 8. here jsperf test used: http://jsperf.com/instanceof-8-times-vs-9-times does have idea why might happen? seems specific instanceof . not happen if else object, example check property. note: filed bugzilla bug this. jan de mooij mozilla team has posted details in bugzilla thread . here's simplistic interpretation of highly technical answers: in i < 8 case, firefox smart enough hoist result = t instanceof test; statement out of loop (according tests, doesn't seem omit altogether). in i < 9 case, apparently doesn't optimization . why? reason not clear, related fact 9 iterations threshold above function considered "hot" enough run through jit compiler. i < 8 cas...
Read more

Getting gateway time-out Rails app with Nginx + Puma running on Digital Ocean -

following this guide setup app on digital ocean droplet, not working. site not loading , it's throwing: "gateway time-out". the puma server works, since ps aux | grep puma prints: root 15878 0.0 0.4 376832 2168 ? sl 12:50 0:00 puma 2.13.4 (unix:///var/www/myapp/shared/tmp/sockets/myapp-puma.sock) [20150930164940] root 15881 0.0 0.7 903676 3692 ? sl 12:50 0:06 puma: cluster worker 0: 15878 [20150930164940] root 24654 0.0 0.1 11748 916 pts/2 s+ 18:00 0:00 grep --color=auto puma my nginx config: user root; worker_processes 1; events { worker_connections 1024; } http { upstream puma { server unix:///var/www/myapp/shared/tmp/sockets/myapp-puma.sock; } server { listen 80; server_name myapp.com; root /var/www/myapp/current/public; access_log /var/www/myapp/current/log/access.log; error_log /...
Read more