Hi everyone, I have a dataset that contains depths measurements every 30 sec for several days.
The subset of data that I am working on looks like this: Date Day Depth 18442.00 29 41.0 18442.00 29 43.5 ... 18442.04 29 40.3 18442.04 29 35.1 ... 18443.00 30 16.5 ... Since my data is collected every 30 sec, I want to find the maximum depth recorded for each day and recorded daily maximum depths into a new array. Now, I would like to also sample the date for each maximum depth value. So far I have been able to sample the max daily depth in a 1-column array using the loop below. I tried creating a new empty array for recording the date for each daily max depth value, but it doesn't seem to be working... Any ideas or suggestions? DF <- data.frame(date,day,depth) samplesperday <- 2*60*24 # number of datapoints per day (2880 here) nbdays<- nrow(DF)/samplesperday # number of days in the dataset (5 here) MaxDepth <- array(NaN,c(nbdays,1)) # create empty array where max depth values will be stored Date <- array(NaN,c(nbdays,1)) # create empty array where date for max depth values will be stored for (i in 1:nbdays){ dayIndex1 <- samplesperday*(i-1)+1 # start of day period (value 1 of 2880) dayIndex2 <- samplesperday*(i) # end of day period (value 2880 of 2880) MaxDepth[i] <- max(DF$depth[dayIndex1:dayIndex2]) # extract max depth value from the 2880 datapoints collected per day Date [i] <- DF$date[MaxDepth[i]] ### NOT WORKING... } Another way to do this, since I am getting one daily max depth value, would be to sample the date every day. Since I have 2880 measurements per day, I would just have to sample the date every 2881 rows. This said, I am stuck and can't figure out out to do this... Your help would be most appreciated! :) Thanks, Fabrice -- View this message in context: http://r.789695.n4.nabble.com/How-to-extract-value-for-specific-rows-in-an-array-tp4655323.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@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.