Hi Philip,
My fault for assuming that what worked for the sample data would work
for the entire data set. If you run the following code:
# read the file into a data frame
phdf<-read.csv("phdf.csv",stringsAsFactors=FALSE)
print(dim(phdf))
# create a logical variable for the subsetting step
keep<-rep(TRUE,length(phdf$Speed))
# this follows the conventional for(i in ...) syntax
# mini (minute index) is the name of the variable
# that is assigned the successive values of the
# unique values in the Minute column of phdf
# here I was lazy and only dealt with the sample data
# what I should have done was to create a column
# with minute values that don't repeat
phdf$hourmin<-phdf$Hour.Z * 60 + phdf$Minute
for(mini in unique(phdf$hourmin)) {
# mark all minutes that are all zeros for deletion
if(all(phdf$Speed[phdf$hourmin == mini] == 0))
keep[phdf$hourmin == mini]<-FALSE
# but now there is another condition
# that I didn't notice (more laziness)
# drop minutes containing ten consecutive zeros
# I'll use a cheap trick for this
# if the length of the run length encoding (rle)
# of the Speed == 0 condition is less than three,
# then there can't be a broken run of zeros
if(length(rle(phdf$Speed[phdf$hourmin == mini])$length)<3)
keep[phdf$hourmin == mini]<-FALSE
}
# now drop any rows for which has marked FALSE (note all caps!)
phdf<-phdf[keep,]
print(dim(phdf))
You will see that it has removed 67 rows. This is the same as if I had
only applied the first "all zeros" condition, for there were no
unique minutes with 11 observations that contained a single non-zero
speed value. I can see that you are getting short runs of zero speeds
near the end. I assume that this is due to the balloon slowly bumping
along the ground. Often just looking at the data can suggest solutions
to problems like this.
Coincidentally I am about to email an old friend of mine whose sons
have dabbled in sending balloons high into the air and I will let them
know that they are not alone in performing this unusual practice. If I
haven't answered all your questions, feel free to let me know.
Jim
On Sun, Aug 16, 2020 at 4:39 AM Philip <herd_dog at cox.net> wrote:
Thanks for getting back to me so quickly.
I can get your code to run without errors but I'm not sure what it
accomplishes since I still get 813 rows of data and 11 variables. The
entire file for a January flight is attached. Also attached is a .jpg of a
flight from a couple of years ago where my wife putzed back and forth across
a road for over an hour by going up or down to catch different winds. Stuff
like this is one of the charms of the sport for those of us who are easily
amused.
keep <- rep(TRUE,length(phdf$Speed)) #813 repetitions of TRUE
for(mini in unique(phdf$Minute))
if(all(phdf$Speed[phdf$Minute==mini]==0))
keep[phdf$Minute==mini]<-False #813 repetitions of
TRUE in the keep data file.
#Don't understand the assignment (<-) to FALSE
phdf <- phdf[keep,] #Still have 813 rows of data.
As you may know, we lay out the balloon and then blow cold air into the
envelope with a gas powered fan. When it is packed we "go hot". Just
before we turn on the pilot light and hit the burner we will turn on the
tracking software which results in several minutes of no movement at the
beginning of the flight. This is what is happening between rows 2 and 70 of
the attached spreadsheet. You will also notice that the balloon slowly
accelerates between rows 71 and 79 p to about 3.4 MPH just after liftoff.
The no movement is what I want to eliminate.
Can you let me know what I am missing.
Two more thing. I really not sure about the:
for(mini in unique(phdf$Minute))
.....line of code. I understand the unique function but not the "mini
in..." part. Is mini a function or just a label? I understand stuff like:
for(i in 1:5) print(1:i)
.....from the R base documentation but not real sure how it fits in here.
And finally, I'm retired, So I have plenty of time and determined to learn
R. But I keep running into things like the "mini in unique" command. I
have read four or five books and watched or read dozens of tutorials but
there always seems to be another layer that alludes me. Any suggestions?
Philip