r 找到带有过滤器的行然后替换单个单元格值

Question

I have data in the following format:

        col1   col2  col3  col4
row1     xx    100    ABC
row2     xx    10     ABC
row3     xx    100    BYZ

And need to find a specific value by multiple conditions and multiply it. I wish to take the 10 value in col2 and row2 and multiply it by 100.

The data frame is too large and will change with each refresh so the problematic value must be found by searching for conditions.

The code I have used to find our desired value is:

dplyr::filter(data, col3 == 'ABC' & col1 == 'xx')[2]

But attempting to re-assign this like so:

dplyr::filter(data, col3 == 'ABC' & col1 == 'xx)[2]
<- dplyr::filter(data, col3 == 'ABC' & col1 == 'xx')[2]
 * 100

Is met with a new error that filter()<- is not a subset function of dplyr.

I tried reverting back to an earlier version of dplyr without improvement.

Answer 1

You can use simple ifelse to change the values in col2 for specific conditions.

library(dplyr)
data %>% mutate(col2 = ifelse(col3 == 'ABC' & col1 == 'xx', col2 * 100, col2))

Or keeping it in base :

transform(df, col2 = ifelse(col3 == 'ABC' & col1 == 'xx', col2 * 100, col2))

Also there is no filter<- function defined so you can't use it directly.