I am trying to calculate monthly means by year of phosphates and nitrates from a
multi year data set. Can anybody help me out with the most effective way to do
this?
My data looks like this:
Collection_Date Test.Name Value
2000-01-24 17:00:00 Phosphate 0.108
2000-01-24 17:00:00 Nitrate 0.037
2001-11-12 08:45:00 Phosphate 0.45
...
Thanks and sorry for the blatantly "newbie" question.
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On Tue, 2011-03-15 at 07:24 -0700, Carl Nim wrote:> I am trying to calculate monthly means by year of phosphates and nitrates from a multi year data set. Can anybody help me out with the most effective way to do this? > > My data looks like this: > > Collection_Date Test.Name Value > 2000-01-24 17:00:00 Phosphate 0.108 > 2000-01-24 17:00:00 Nitrate 0.037 > 2001-11-12 08:45:00 Phosphate 0.45 > ... > > > Thanks and sorry for the blatantly "newbie" question.Let's say you have a data.frame, mydata, with the above data. Then you could write a function mymean <- function(year, month, substance) { mysub <- subset(mydata, format(as.PPSIXlt.date(Collection_Date), "%Y") == year, format(as.POSIXlt.date(Collection_Date), "%b") == month, Test.Name == substance) return(mean(mysub$value)) } Then you need to apply this function to every combination of year, month and substance in your data.frame. You can do this by M <- expand.grid(2000:2010, month.abb, c("Phosphate", "Nitrate")) meanValues <- apply(M, 1, mymean(myRowEntry[1], myRowEntry[2], myRowEntry[3]) In the end you can put the result together with M, i.e. M <- cbind(M, meanValues)> > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.-- Daniel Kaschek Physikalisches Institut, Freiburg Hermann-Herder-Str. 3 79104 Freiburg Office: Westbau, 02020 Phone: +49-761-203-8531 -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 490 bytes Desc: This is a digitally signed message part URL: <https://stat.ethz.ch/pipermail/r-help/attachments/20110315/ab04e7ce/attachment.bin>
You could use the by() function after a little data manipulation.
The first line will create a field just of the date portion of your datetime
field. Then you can use the by() function to use the indices you desire to
calculate the mean.
mSamp$cDT <- chron(unlist(strsplit(as.character(mSamp$Collection_Date),
split=" "))[seq(1,nrow(mSamp),2)], format="y-m-d",
out.format="m/d/y")
with(mSamp, by(Value, list(years(cDT), months(cDT)), mean, na.rm=TRUE))
I like using the chron package for my dates and times.
Adrian
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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Carl Nim
Sent: Tuesday, March 15, 2011 10:25 AM
To: r-help at r-project.org
Subject: [R] Calculate monthly means
I am trying to calculate monthly means by year of phosphates and nitrates from a
multi year data set. Can anybody help me out with the most effective way to do
this?
My data looks like this:
Collection_Date?????????????????? Test.Name????????????? Value
2000-01-24 17:00:00??????????? Phosphate?????????????? 0.108
2000-01-24 17:00:00??????????? Nitrate???????????????????? 0.037
2001-11-12 08:45:00??????????? Phosphate?????????????? 0.45
...
Thanks and sorry for the blatantly "newbie" question.
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