Waiting until value changes to make calculation-CodePudding

I have the following dataframe:

time <- c(1,2,3,4,5,6,7,8,9,10,11,12)
threshold <- c(1,1,1,0,0,2,2,1,1,2,2,0)
value <- c(5,3,2,4,6,9,1,10,3,5,2,4)

df <- data.frame(time, threshold, value)

The logic behind the threshold variable is that when there is a 1: store the first value (5) and subtract the number when the threshold changes (4). During the first threshold period of "1", the calculation would be 5 - 4 = 1, which should be stored in a new column at time t=4.

Threshold "0" means no calculation.

Threshold "2" means just the reverse of "1", where the the initial value 9 is subtracted by 10.

The goal would be a table like this:

Is there a way to calculate perform this calculation in R?

CodePudding user response：

If you use the rle function, you can focus on rows where there is a threshold change. Then, align the values to be subtracted and translate the threshold to a factor controlling the sens of the subtraction.

#Select only rows with a threshold change,
# based on https://stackoverflow.com/a/27482738/14027775
compact_threshold <- rle(df$threshold)
row_ids <- cumsum(c(1, compact_threshold$lengths[-length(compact_threshold$lengths)]))

#Transform thresholds to a factor 
# if the row is in a threshold change
df$subFactor <- df$threshold
df$subFactor[-row_ids] <- NA
df$subFactor[df$subFactor==0] <- NA
df$subFactor[df$subFactor==2] <- -1

#Align each value with the one 
# corresponding to the next threshold change
df$value2 <- NA
df$value2[row_ids] <- c(df$value[row_ids][-1], NA)

df$calculation <- (df$value-df$value2)*df$subFactor
#Shift results to the next threshold
df$calculation[row_ids] <- c(NA, df$calculation[row_ids][-length(row_ids)])

df <- df[,c("time", "threshold", "value", "calculation")]
df
#   time threshold value calculation
#1     1         1     5          NA
#2     2         1     3          NA
#3     3         1     2          NA
#4     4         0     4           1
#5     5         0     6          NA
#6     6         2     9          NA
#7     7         2     1          NA
#8     8         1    10           1
#9     9         1     3          NA
#10   10         2     5           5
#11   11         2     2          NA
#12   12         0     1          -4

Raw data

#Data
time <- c(1,2,3,4,5,6,7,8,9,10,11,12)
threshold <- c(1,1,1,0,0,2,2,1,1,2,2,0)
value <- c(5,3,2,4,6,9,1,10,3,5,2,1)

df <-  data.frame(time, threshold, value)
df
#   time threshold value
#1     1         1     5
#2     2         1     3
#3     3         1     2
#4     4         0     4
#5     5         0     6
#6     6         2     9
#7     7         2     1
#8     8         1    10
#9     9         1     3
#10   10         2     5
#11   11         2     2
#12   12         0     1