使用ifelse if R增加向量中变量的值

Question

I have an ifelse statement and want to increase the the variable by 1 each time the condition is met and drop the count to by subtracting the entire count -count if the condition is not met.

df = data.frame(indicator= c(60,61,58,40,70,80))

position = 0
df$sig = ifelse((df$indicator > 60), 
       (position = position + 1), 
       -position)

The answer would look like this

df = data.frame(indicator= c(60,61,58,40,70,80),
                sig = c(0,1,0,0,1,2))

This is to keep track of a trading position (buy if over 60 and sell if under but keep track of how big the position is.

How can I do this in R?

Answer 1

Maybe like this, with dplyr and rleid from the data.table package:

df = data.frame(indicator= c(60,61,58,40,70,80))

library(dplyr)
library(data.table)
df %>%
  group_by(group = rleid(indicator > 60)) %>%
  mutate(sig = cumsum(indicator > 60)) %>% 
  ungroup() %>%
  select(-group) %>%
  as.data.frame

Output:

  indicator sig
1        60   0
2        61   1
3        58   0
4        40   0
5        70   1
6        80   2

---

Or alternatively, only with data.table :

df = data.frame(indicator= c(60,61,58,40,70,80))

library(data.table)
setDT(df)[,sig := cumsum(indicator > 60), rleid(indicator > 60)]

Hope this helps!

Answer 2

With vanilla R, you can use rle and ave + cumsum :

rl <- rle(df$indicator > 60)
rl$values <- seq_along(rl$values)

df$sig <- ave(df$indicator, inverse.rle(rl), FUN = function(x) cumsum(x > 60))

The result:

> df
  indicator sig
1        60   0
2        61   1
3        58   0
4        40   0
5        70   1
6        80   2

Answer 3

count = 0
count = count + sum(ifelse(df$colour == "green", 1, 0))

However you could more directly just do this:

count = sum(df$colour == "green")

This works because TRUE is equal to 1 and FALSE is equal to 0 when you sum them.

Answer 4

That would be:

position <- 0

df <- data.frame(indicator= c("60","61","58","40","70","80"))
df$indicator <- as.numeric(df$indicator)

df_sum <- sum(df$indicator)

position <- ifelse(df_sum > 60, position + 1, position -1)