Hi guys, recently I made a post about creating a new data frame, and I got that settled.

Now, I'm trying to use the new column to store results for each row.

For example: let's say I have two existing columns (time and interval) and a 3rd empty column.

I want to find the difference of time by subtracting consecutive values.

df[i, 3] <- df[i, 1] - df[i-1, 1]

by itself, for example, I can use it. For example:

df[4,1] - df[3,1] will give me a result.

I want to input this answer into the same row of the new column. And do this for all rows.

But it won't let me because it says:

replacement has length zero.

what should I do to solve this issue? thank you.