apply and cousins

John:

1. Please read and follow the posting guide. In particular, provide a
small reproducible example so that we know what your data and looping
code look like.

2. apply-type commands are *not* vectorized; they are disguised loops
that may or may not offer any speedup over explicit loops.

3. A guess at a possible strategy is to convert character date-time
data to POSIXct dates using as.POSITct and then just choose those rows
with the maximum value . e.g.

x[x==max(x)]

These operations *are* vectorized.

However, this guess might be completely useless with your unspecified
data, so beware.

Cheers,
Bert

Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Wed, Jun 8, 2016 at 9:41 AM, John Logsdon

Folks

Is there any way to get the row index into apply as a variable?

I want a function to do some sums on a small subset of some very long
vectors, rolling through the whole vectors.

apply(X,1,function {do something}, other arguments)

seems to be the way to do it.

The subset I want is the most recent set of measurements only - perhaps a
couple of hundred out of millions - but I can't see how to index each
value.  The ultimate output should be a matrix of results the length of
the input vector.  But to do the sum I need to access the current row
number.

It is easy in a loop but that will take ages. Is there any vectorised
apply-like solution to this?

Or does apply etc only operate on each row at a time, independently of
other rows?


Best wishes

John

John Logsdon
Quantex Research Ltd
+44 161 445 4951/+44 7717758675

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