Double sliding window - r

Question

I want to create a double sliding window in a for loop. An example data set might look like:
a <- structure(list(a = c(0.0961136, 0.1028192, 0.1106424, 0.1106424,
0.117348, 0.117348, 0.117348, 0.122936, 0.1307592, 0.1307592,
0.1318768, 0.1318768, 0.1385824, 0.1385824, 0.1318768, 0.1251712,
0.1251712, 0.1251712, 0.1251712, 0.1251712)), .Names = "a", row.names = c(NA,
-20L), class = "data.frame")
The code I have so far looks like this:
windowSize <- 5
windowStep <- 1
dat <- list()
for (i in seq(from = 1, to = nrow(a), by = windowStep)){
window1 <- a[i:windowSize, ]
window2 <- a[i:windowSize + windowSize, ]
if (median(window1) <= 0.12 && (median(window1) >= 0.08)) {
p <- "True"
} else
p <- "not"
dat[[i]] <- c(p)
}
result <- as.data.frame(do.call(rbind, dat))
This example shows that I require two windows of size 5 (data points) to slide one in front of the other by 1 data point at a time. This example does not utilize window 2 because it doesn't work!(I will need it to work eventually) However using just window1 to calculate the median (in this case) at each step works but the output is incorrect. The if statements ask that if the median of window 1 is between 0.08 and 0.12 then output "True" else "not."
Output for my for loop =
1 True
2 True
3 True
4 True
5 True
6 True
7 True
8 True
9 True
10 not
11 not
12 not
13 not
14 not
15 not
16 not
17 not
18 not
19 not
20 not
Correct output as checked using rollapply (and obviously can be seen by eye)
rollapply(a, 5, FUN = median, by = 1, by.column = TRUE, partial = TRUE, align = c("left"))
should be:
1 True
2 True
3 True
4 not
5 not
6 not
7 not
8 not
9 not
10 not
11 not
12 not
13 not
14 not
15 not
16 not
17 not
18 not
19 not
20 not
Could the solution remain as a for loop if possible as I have much more to add but need to get this right first. Thanks.

Answer 1

This gets close..modified from: https://stats.stackexchange.com/questions/3051/mean-of-a-sliding-window-in-r
windowSize <- 10
windowStep <- 1
Threshold <- 0.12
a <- as.vector(a)
data <- a
slideFunct <- function(data, windowSize, WindowStep){
total <- length(data)
dataLength <- seq(from=1, to=(total-windowSize), by=windowStep)
result <- vector(length = length(dataLength))
for(i in 1:length(dataLength)){
result[i] <- if (median(data[dataLength[i]:(dataLength[i]+windowSize)]) <= Threshold)
result[i] <- "True"
else
result[i] <- "not"
}
return(result)
}