根据趋势分配组

Question

I have searched a lot for this simple question, but have not found a solution. It looks really simple. I have a dataframe with a column like this:

Value
0.13
0.35
0.62
0.97
0.24
0.59
0.92
0.16
0.29
0.62
0.98

All values have a range between 0 and 1. What I want is that when the value starts to drop, I assign a new group to it. Within each group, the value is increasing. So the ideal outcome will look like this:

Value Group
0.13   1
0.35   1
0.62   1
0.97   1
0.24   2
0.59   2
0.92   2
0.16   3
0.29   3
0.62   3
0.98   3

Does anyone have a suggestion for how to address this?

Answer 1

This should do the trick, and uses only vectorised base functions. You may want to exchange the < for <= , if thats the behaviour you wanted.

vec <- c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98)

cumsum(c(1, diff(vec) < 0))

Answer 2

This isn't the most elegant solution, but it works:

value <- c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98)

foo <- data.frame(value, group = 1)
current_group <- 1
for(i in 2:nrow(foo)){
  if(foo$value[i] >= foo$value[i-1]){
    foo$group[i] <- current_group
  }else{
    current_group <- current_group + 1
    foo$group[i] <- current_group
  }
}

Answer 3

df <- data.frame( x = c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98))
df$y <- c(df$x[-1], NA)  # lag column
df$chgdir <- as.numeric(df$y - df$x < 0)  # test for change in direction
df$chgdir[is.na(df$chgdir)] <- 0  # deal with NA
df$group <- cumsum(df$chgdir) + 1  # determine group number
df[,c("x", "group")]
#>       x group
#> 1  0.13     1
#> 2  0.35     1
#> 3  0.62     1
#> 4  0.97     2
#> 5  0.24     2
#> 6  0.59     2
#> 7  0.92     3
#> 8  0.16     3
#> 9  0.29     3
#> 10 0.62     3
#> 11 0.98     3