Message-ID: <Pine.A41.4.44.0208010810140.18384-100000@homer26.u.washington.edu>
Date: 2002-08-01T15:15:35Z
From: Thomas Lumley
Subject: Help massaging big arrays
In-Reply-To: <20020801143824.GA5932@phil.chu.com.au>
On Fri, 2 Aug 2002, Philip Rhoades wrote:
> Hi all,
>
> I hope someone can give me some quick pointers - it would take me ages
> to work this out from scratch - I want to:
>
> - From an array - 32 cols x 1000 rows of small floats
Call it X
> - Produce a second array from the first where the all numbers have an
> abs fn applied to them (to get rid of the neg numbers)
X <- abs(X)
> - Produce a third array from the second where all numbers less than
> 0.0005 are converted to 0.0005
X[X<0.005] <- 0.005
> - Produce a fourth array (5x1000) from the third where the first number
> in the row is the mean of the first two numbers of array #3, the second
> number is the mean of the first 4 numbers, 3rd mean of 8, 4th mean of
> 16, 5th mean of 32
Y<-matrix(ncol=5,nrow=1000)
for(i in 1:5)
Y[,i] <- rowMeans(X[ ,1:(2^i)])
> - Produce a fifth (5x1000) array by dividing array #4 into another
> 5x1000 array
Y <- Z/Y
> - Produce 5 means of the 5 columns of array #5
colMeans(Y)
-thomas
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