I have the following data
head(datakurz)
Datum Abfluss days
1 1968-01-01 0.681 1968-01-01
2 1968-01-02 0.610 1968-01-02
3 1968-01-03 0.610 1968-01-03
4 1968-01-04 0.790 1968-01-04
5 1968-01-05 0.904 1968-01-05
6 1968-01-06 3.720 1968-01-06
....
....
....
I want to calculate the min values of each 5 rows , so basically
min of (0.681,0.610,0.610,0.790,0.904) = 0.610
this is done by my function
Datum <- datad$days[1:100]
Abfluss <- datad$q[1:100]
datakurz <- data.frame(Datum, Abfluss)
datakurz$days <- as.Date(datakurz$Datum, format="%Y-%m-%d")
class(datakurz$days)
head(datakurz)
# Blöcke gleicher Größe (window size) und deren Minima berechnen
#minimum <- numeric(ws)
zaehler <- nrow(datakurz) / 5 #Anzahl Zeilen Datensatz durch ws teilen -> Anzahl Blöcke
azeile <- 1
ezeile <- 5
for(i in 1:zaehler){
minimum <- min(datakurz$Abfluss [azeile:ezeile])
print(minimum)
azeile <- azeile+5
ezeile <- ezeile+5
}
This generates the following output
[1] 0.61
[1] 0.828
[1] 0.681
[1] 1.41
[1] 0.79
[1] 0.904
[1] 0.828
[1] 0.718
[1] 0.904
[1] 0.79
[1] 0.944
[1] 1.03
[1] 0.866
[1] 1.07
[1] 1.07
[1] 1.25
[1] 0.944
[1] 0.828
[1] 0.79
[1] 1.07
so basically 0.61 is the min of the first 5 values 0.828 is the min value of the next block auf 5 values and so on...
Now I want to append these values as a column to the data frame, but just the min. value of each block of 5 values (the rest should be null)
Desired output
Datum Abfluss days min
1 1968-01-01 0.681 1968-01-01 NULL
2 1968-01-02 0.610 1968-01-02 0.610
3 1968-01-03 0.610 1968-01-03 0.610
4 1968-01-04 0.790 1968-01-04 NULL
5 1968-01-05 0.904 1968-01-05 NULL
6 1968-01-06 3.720 1968-01-06 ...
Anyone can help me?
You can use ave to find the min for a group of 5.
D$min <- ave(D$q, (seq_len(nrow(D))-1) %/% 5, FUN=function(x)
ifelse(x==min(x), x, NA))
D
# q min
#1 1 1
#2 2 NA
#3 3 NA
#4 4 NA
#5 5 NA
#6 6 6
#7 7 NA
#8 8 NA
#9 9 NA
#10 10 NA
#11 11 11
#12 12 NA
#13 13 NA
#14 14 NA
#15 15 NA
Data:
D <- data.frame(q=1:15)