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10080355
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2012-04-09T21:52:56.300
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2012-04-10T20:34:48.617
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2017-05-23T12:18:06.173
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text
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I can't think of an obvious simple solution, but, having looked at the suggestions (particularly <a href="https://stackoverflow.com/users/202229/smci">smci</a>'s suggestion of using <code>rle</code>) I came up with a complicated function that appears to be more efficient. This is the code, I'll explain below: <pre><code># Your function your.func = function(dat) { na.pos <- which(is.na(dat)) if (length(na.pos) == length(dat)) { return(dat) } non.na.pos <- setdiff(seq_along(dat), na.pos) nearest.non.na.pos <- sapply(na.pos, function(x) which.min(abs(non.na.pos - x))) dat[na.pos] <- dat[non.na.pos[nearest.non.na.pos]] dat } # My function my.func = function(dat) { nas=is.na(dat) if (!any(!nas)) return (dat) t=rle(nas) f=sapply(t$lengths[t$values],seq) a=unlist(f) b=unlist(lapply(f,rev)) x=which(nas) l=length(dat) dat[nas]=ifelse(a>b,dat[ ifelse((x+b)>l,x-a,x+b) ],dat[ifelse((x-a)<1,x+b,x-a)]) dat } # Test n = 100000 test.vec = 1:n set.seed(1) test.vec[sample(test.vec,n/4)]=NA system.time(t1<-my.func(test.vec)) system.time(t2<-your.func(test.vec)) # 10 times speed improvement on my machine # Verify any(t1!=t2) </code></pre> My function relies on <code>rle</code>. I am reading the comments above but it looks to me like <code>rle</code> works just fine for <code>NA</code>. It is easiest to explain with a small example. If I start with a vector: <pre><code>dat=c(1,2,3,4,NA,NA,NA,8,NA,10,11,12,NA,NA,NA,NA,NA,18) </code></pre> I then get the positions of all the NAs: <pre><code>x=c(5,6,7,8,13,14,15,16,17) </code></pre> Then, for every "run" of NAs I create a sequence from 1 to the length of the run: <pre><code>a=c(1,2,3,1,1,2,3,4,5) </code></pre> Then I do it again, but I reverse the sequence: <pre><code>b=c(3,2,1,1,5,4,3,2,1) </code></pre> Now, I can just compare vectors a and b: If a<=b then look back and grab the value at x-a. If a>b then look ahead and grab the value at x+b. The rest is just handling the corner cases when you have all NAs or NA runs at the end or the start of the vector. There is probably a better, simpler, solution, but I hope this gets you started.
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1. POReplacing NAs in R with nearest value
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