根据先前的行替换R中的行值

Question

Below is my data frame df

df <- data.frame(A=c(1,1,1,1,0,0,-1,-1,-1,1,1,1,1))

I would like to have another variable T_D which maintains the first value when it encounters the change in the value of A by either 1 or -1 and replaces the next rows by 0

Expected Output:

A  T_D
1  1
1  0
1  0
1  0
0  0 
0  0
-1 -1
-1  0
-1  0 
1  1
1  0  
1  0
1  0   

Answer 1

Base R solution, this seems to work for you:

df$T_D = df$A*!c(FALSE,diff(df$A,lag=1)==0),

Find the difference between sequential rows. If the difference is 1, take the entry from column A, otherwise set to 0.

OUTPUT

    A T_D
1   1   1
2   1   0
3   1   0
4   1   0
5   0   0
6   0   0
7  -1  -1
8  -1   0
9  -1   0
10  1   1
11  1   0
12  1   0
13  1   0

Answer 2

dplyr 's window functions make this easy. You can use the lag function to look at the previous value and see if it equals the current value. The first row of the table doesn't have a previous value so T_D will always be NA . Fortunately that row will always be equal to a so it's an easy problem to fix with a second mutate (or df[1,2] <- df[1,1] ).

library(tidyverse) # Loads dplyr and other useful packages

df <- tibble(a = c(1, 1, 1, 1, 0, 0, -1, -1, -1, 1, 1, 1, 1))

df %>%
  mutate(T_D = ifelse(a == lag(a), 0, a)) %>%
  mutate(T_D = ifelse(is.na(T_D), a, T_D))

Answer 3

df$T_D <- sign(abs(df$A)*diff(c(0, df$A)))

Answer 4

A data.table approach would be,

library(data.table)
setDT(df)[, T_D := replace(A, duplicated(A), 0), by = rleid(A)][]

#     A T_D
# 1:  1   1
# 2:  1   0
# 3:  1   0
# 4:  1   0
# 5:  0   0
# 6:  0   0
# 7: -1  -1
# 8: -1   0
# 9: -1   0
#10:  1   1
#11:  1   0
#12:  1   0
#13:  1   0