Detect frequently changing values

user_5596534 0
Viewed 41

I am trying to construct a boolean for the following question:

For a given group did cond change values more than X times? Here is some sample data:

df <- rbind(
  data.frame(
    cond = c("cond1", "cond2", "cond1", "cond2", "cond3"),
    day = 1:5,
    group = "group1"
  ),
  data.frame(
    cond = c("cond1", "cond1", "cond1", "cond1", "cond2"),
    day = 1:5,
    group = "group2"
  )
)

df
#>     cond day  group
#> 1  cond1   1 group1
#> 2  cond2   2 group1
#> 3  cond1   3 group1
#> 4  cond2   4 group1
#> 5  cond3   5 group1
#> 6  cond1   1 group2
#> 7  cond1   2 group2
#> 8  cond1   3 group2
#> 9  cond1   4 group2
#> 10 cond2   5 group2

The ordering is relevant here hence the day variable. But I am just trying to figure out how to detect when cond changes alot and then return those rows. Ideally will be fitting this into a group_by then filter idiom but really I'm not sure how to construct the boolean.

r
3 Answers

You may create a "change" variable using ave, then subset on some value of it.

transform(df, change=ave(as.numeric(gsub('\\D', '', cond)), group, FUN=\(x) sum(diff(x) != 0))) |>
  subset(change < 4)
#     cond day  group change
# 6  cond1   1 group2      1
# 7  cond1   2 group2      1
# 8  cond1   3 group2      1
# 9  cond1   4 group2      1
# 10 cond2   5 group2      1
user_65740380

I am not sure if this is meant. But if you want to know now many times cond changes within each group, we could do:

library(dplyr)

df %>% 
  group_by(group) %>% 
  mutate(change = max(cumsum(cond != lag(cond, def=first(cond)))))

   cond    day group  change
   <chr> <int> <chr>   <int>
 1 cond1     1 group1      4
 2 cond2     2 group1      4
 3 cond1     3 group1      4
 4 cond2     4 group1      4
 5 cond3     5 group1      4
 6 cond1     1 group2      1
 7 cond1     2 group2      1
 8 cond1     3 group2      1
 9 cond1     4 group2      1
10 cond2     5 group2      1
user_133216470

We may create the logic by comparing the current with previous values after grouping

library(dplyr)
n <- 3
df %>%
   group_by(group) %>%
   filter(sum(cond != lag(cond), na.rm = TRUE) >= n) %>%
   ungroup

-output

# A tibble: 5 × 3
  cond    day group 
  <chr> <int> <chr> 
1 cond1     1 group1
2 cond2     2 group1
3 cond1     3 group1
4 cond2     4 group1
5 cond3     5 group1

Or if it is not just adjacent element, then use rle

df %>% 
  group_by(group) %>% 
 filter(length(rle(cond)$lengths) > n) %>% 
 ungroup

Or using data.table

library(data.table)
setDT(df)[, if(uniqueN(rleid(cond)) > n) .SD,.(group)]
user_37322710
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