在 R - 如果单元格值与列匹配，则返回值，否则在新的 dataframe 中为 0

Question

B1  B2  total
10  0   10
20  20  40
0   20  20
10  20  30

Using the dataframe above, I want to create a new dataframe with the following logic:

Going by rows, if cells (B1:B2) matches d$total, return cell value, else 0.

To look like this

B1   B2
10   0
0    0
0    20
0    0

What is the best way to do this in R?

Thank you.

Answer 1

You can turn the values to 0 where total does not match values in first two columns.

df1 <- df[1:2]
df1[df1 != df$total] <- 0
df1

#  B1 B2
#1 10  0
#2  0  0
#3  0 20
#4  0  0

Answer 2

Here's a tidyverse way:

library(tidyverse)

df <- tribble(
  ~ B1, ~ B2, ~ total,
  10,  0,   10,
  20,  20,  40,
  0,   20,  20,
  10,  20,  30
)

df %>%
  mutate(
    B1 = if_else(B1 == total, B1, 0),
    B2 = if_else(B2 == total, B2, 0)
  ) %>%
  select(B1, B2)
#> # A tibble: 4 x 2
#>      B1    B2
#>   <dbl> <dbl>
#> 1    10     0
#> 2     0     0
#> 3     0    20
#> 4     0     0

^{Created on 2020-11-25 by the reprex package (v0.3.0)}