Iterating down a column HELP!

[Adrian]

hello, i am wondering why this code is not working. So i have a table of close prices and i am trying to create a new column called 'triangle' where if the close price of next line is greater than the close price the previous one, assign a value of 2 else assign a value of 1. I am getting an argument of length zero and i do not understand why

for(n in 2:nrow(data)) {
  if(data[n]$Close > data[n+1,]$Close) {
    data$triangle[n] <- 1
  }
  else
  {
    data$triangle[n] <- 2
  }
}

[cderv]

Hello,

Please can you follow the advice on FAQ: Tips for writing R-related questions.

You'll see a reprex will help. Currently, we have no idea about what data is and you error may comes from it and how you test it in if.

[StatSteph]

Your current code is likely not working because your n gets out of bounds. When you are on your last value of n, you try to access data[nrow(data)+1, ]$Close but that doesn't exist. You might want your loop to go from 1:(nrow(data)-1)

I would use the lag or lead function to solve as shown here - it's a bit unclear which one you want but one of these two examples should be it:

library(tidyverse)

data <- tibble(Close=c(1, 2, 3, 5, 4, 6, 2, 2)) %>%
  mutate(if_else(Close < lead(Close), 2, 1))
data
#> # A tibble: 8 x 2
#>   Close `if_else(Close < lead(Close), 2, 1)`
#>   <dbl>                                <dbl>
#> 1     1                                    2
#> 2     2                                    2
#> 3     3                                    2
#> 4     5                                    1
#> 5     4                                    2
#> 6     6                                    1
#> 7     2                                    1
#> 8     2                                   NA

data <- tibble(Close=c(1, 2, 3, 5, 4, 6, 2, 2)) %>%
  mutate(if_else(Close > lag(Close), 2, 1))
data
#> # A tibble: 8 x 2
#>   Close `if_else(Close > lag(Close), 2, 1)`
#>   <dbl>                               <dbl>
#> 1     1                                  NA
#> 2     2                                   2
#> 3     3                                   2
#> 4     5                                   2
#> 5     4                                   1
#> 6     6                                   2
#> 7     2                                   1
#> 8     2                                   1

^{Created on 2020-01-13 by the reprex package (v0.3.0)}