Is there a funct to sum differences?

Thanks a lot everyone for the help.  I will fall silent for quite some time now as I try to understand what you've put before me.

Yes, my first problem is a lack of understanding of vector and matrix arithmetic.  So I have a bit of a learning curve.

Another mistake I made was not giving you sample input with a variety of numbers in it.  I can see quite clearly. Makes it hard to tell if a routine is working properly when everything is zeroes. That was unthinking - my usual habit - I simply took the first items from the list because they included the column headers.  I could easy have cut and pasted something else in there.

And I forgot to 'reply everyone' last time, too. Will I never learn..

Jeff, yes your last didn't work for me. I entirely believe that was my implementation of it. With this 'sophisticated' or 'grownup' code I'm largely blundering around in the dark.

Okay, I'll go looking for illumination..

Have a good Xmas.

:)

ab----- Original Message -----

From: Jeff Newmiller <jdnewmil at dcn.davis.ca.us>
To: "Fox, John" <jfox at mcmaster.ca>
Cc: arthur brogard <abrogard at yahoo.com>; "r-help at r-project.org" <r-help at r-project.org>
Sent: Sunday, 25 December 2016, 6:06
Subject: RE: [R] Is there a funct to sum differences?

Assuming John's understanding is correct, you can also do this without for 
loops. It takes getting used to vector and matrix arithmetic, which you
can read more about in the Introduction to R document that comes with R, 
or on R Exercises website [1].

You indicated having a problem with my last reproducible example... it did 
work, if you went through it one step at a time. If you skipped steps, you 
would have problems like you encountered. For completeness, I will give 
the whole reproducible example again here... don't mix in your own steps 
until you have worked through all the steps in this example... or at least 
if you do, go back and step through these steps one at a time if you 
change something that breaks it.

[1] http://r-exercises.com/2015/11/28/matrix-exercises/

#########------ begin
rates <- read.table( text =
"Date          Int
Jan-1959        5
Feb-1959        5
Mar-1959        5
Apr-1959        5
May-1959        5
Jun-1959        5
Jul-1959        5
Aug-1959        5
Sep-1959        5
Oct-1959        5
Nov-1959        5
", header = TRUE, colClasses = c( "character", "numeric" ) )

rates$thisone <- c(diff(rates$Int), NA)
rates$nextone <- c(diff(rates$Int, lag=2), NA, NA)
rates$lastone <- (rates$thisone + rates$nextone)/6.5*1000

rates$experiment1 <- rates$Int + c( rates$Int[ -1 ], NA )
rates$Int2 <- (1:11)^2
rates$experiment2 <- rates$Int2 + c( rates$Int2[ -1 ], NA )

# lag
N <- 5
# see ?embed, or https://en.wikipedia.org/wiki/Embedding
embed( c( rates$Int2, rep( NA, N ) ), N+1 )
# make a matrix of the same size as the embed result
matrix( rep( rates$Int2, N+1 ), ncol=N+1 )
# subtract the first values
embed( c( rates$Int2, rep( NA, N ) ), N+1 ) - rates$Int2
# or can rely on automatic replication ... depends on the
# fact that the embed result is a matrix which is really just
# a vector displayed in folded up form
embed( c( rates$Int2, rep( NA, N ) ), N+1 ) - rates$Int2
# anyway, the result can be computed in one line (wrapped for readability)
rates$experiment3 <- rowSums(   embed( c( rates$Int2
                                         , rep( NA, N )
                                         )
                                      , N+1
                                      )
                               - rates$Int2
                             , na.rm=TRUE
                             )

Is there a funct to sum differences?

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