Look at these functions. They should give you the building blocks you
need:
?diff # returns a vector of length n-1
#it would be a logical vector if wrapped in the appropriate
functions
#needs to be padded to line up with dataframes
?rle # returns a list with the lengths and values of the repeats
# will work on logical vectors
If your data is in a dataframe, snowdepth, with column names time and
depth, then this might create a difference column in that dataframe:
snowdepth$incr <- c(0, diff(snowdepth$depth))
And this might give you the be a noise marker:
snowdepth$noise <- c(FALSE, diff(snowdepth$depth) > x)
You should also look at the function dput so you can offer
reproducible code and data with further questions.
--
David Winsemius
On Mar 5, 2009, at 3:46 AM, Kara Przeczek wrote:
I am fairly new to R and I would like to do the following, but do
not know where to start. Any help or direction would be appreciated.
I have a time series of snow depth measurements. I would like to
determine the depth of snowfall for each snowfall event. There is
noise in the data so I only want to add data values if the
subsequent depth is greater than the previous by a certain margin. I
am only interested in calculating snow accumulation events.
Example data:
Time depth
1 84.3
2 84.5
3 86
4 86.1
5 85.8
6 86.7
7 87.9
8 89.1
9 90
10 89
11 88
12 88
13 89.1
14 90
15 91.2
16 89.9
... ...
I would like to create a second data frame from the data that looks
something like this:
Event InitialDepth FinalDepth Accumulation InitialTime
FinalTime
1 84.3 90 5.7 1 9
2 88 91.2 3.2 11 15
...
I would like to write a program that progresses through the depth
column, point by point, to test if (i+1) - i > x. (where I will set
x to exlude the noise in the data). As long as i+1 is greater than
or equal to i, then the initial depth stays at the first data point
and the final value changes to that in i+n. Once the test is false,
this indicates the end of the event, the accumulation is calculated,
all values are saved as event X and a new event is started.
I tried using ifelse(), but I do not know how to move through the
data and then save the initial and final values and time stamps in
another table.
Thank you very much for your time.
Kara
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
