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readnwisdaily
2017 Dec 18
2
Finding center of mass in a hydrologic time series
Eric B's response provided just the kind of quick & simple solution I was
hoping for (appears as the function com below). However, I once again
failed to take advantage of the power of R and have reverted back to using
a for loop for the next step of the processing. The example below (which
requires the library EGRET for pulling an example dataset) works, but
probably can be replaced
2017 Dec 18
0
Finding center of mass in a hydrologic time series
Hi Eric,
the following works for me.
HTH,
Eric
library(EGRET)
StartDate <- "1990-10-01"
EndDate <- "2017-09-30"
siteNumber <- "10310000"
QParameterCd <- "00060"
Daily <- readNWISDaily(siteNumber, QParameterCd, StartDate, EndDate)
# Define 'center of mass' function
com <- function(x) {
match(TRUE, cumsum(x/sum(x)) > 0.5) -
2017 Dec 16
0
Finding center of mass in a hydrologic time series
Hi Eric,
How about
match( TRUE, cumsum(hyd/sum(hyd)) > .5 ) - 1
HTH,
Eric
On Sat, Dec 16, 2017 at 3:18 PM, Morway, Eric <emorway at usgs.gov> wrote:
> The small bit of script below is an example of what I'm attempting to do -
> find the day on which the 'center of mass' occurs. In case that is the
> wrong term, I'd like to know the day that essentially cuts
2017 Dec 16
3
Finding center of mass in a hydrologic time series
The small bit of script below is an example of what I'm attempting to do -
find the day on which the 'center of mass' occurs. In case that is the
wrong term, I'd like to know the day that essentially cuts the area under
the curve in to two equal parts:
set.seed(4004)
Date <- seq(as.Date('2000-09-01'), as.Date('2000-09-30'), by='day')
hyd <-