Hi,
May be this helps:
val <- with(mydataset, diff(Lat))
indx <- cumsum(c(TRUE,val!=0 & !is.na(val)))
mydataset$Tr[indx==1]
#[1] 3 5 2 5
sum(mydataset$Tr[indx==1])
#[1] 15
mydataset$Tr[indx<=2]
#[1] 3 5 2 5 6
sum(mydataset[indx==6,-2])
#[1] 12.5
#or
sum(mydataset[indx==rev(unique(indx))[2],-2])
[1] 12.5
A.K.
Dear R-Helpers,
I am analyzing a data frame that has the same structure as the example below
("mydataset"):
Ti Tr Lat
1 3 0
2 5 0
3 2 0
4 5 0
5 6 0.1
6 7 0.2
7 1 0.5
8 4 0
9 2.5 0
10 3.5 0
11 2.7 0
12 3.3 0.5
13 5 0
14 4 0
NA NA NA
14 54 5.1
NA NA NA
NA NA NA
I am trying to perform the following tasks:
1. Extraction of all the values of "Tr" before the values of "Lat" differ for
the first time from "0".
mydataset$Tr[mydataset$Lat==0] does obviously not help, because it extracts
every value of "Tr" for "Lat" equal to zero.
In this case ("mydataset") the values to be extracted are: 3.0, 5.0, 2.0, 5.0,
which I would sum to obtain 15.0.
2. Same procedure as above, but including the first non-zero value of "Lat".
"mydataset" values are: 3.0, 5.0, 2.0, 5.0, 6.0 which I would sum (21.0).
3. Extraction of the last value of "Lat" that is different from
"0" and that appears before the first "NA" (in this case "0.5"); sum it
with the corresponding value of "Ti" ("12") to obtain 12.5.
I have spent some time looking around on the web, but I was not able to find
the answers I need.
Any help? Thank you a lot!
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