& is the elementwise operation. But && is the bitwise operation. It’s just easier to see the differences through examples.
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library(dplyr) data <- data.frame(gender = c('m', 'm', 'f', 'm', 'm'), grade = c(1,4,4,2,3)) |
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> data %>% mutate( + new = ifelse(gender == 'm' & grade > 2, "abc","def")) gender grade new 1 m 1 def 2 m 4 abc 3 f 4 def 4 m 2 def 5 m 3 abc |
But if we use &&,
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data %>% mutate( new = ifelse(gender == 'm' && grade > 2, "abc","def")) |
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> data %>% mutate( + new = ifelse(gender == 'm' && grade > 2, "abc","def")) gender grade new 1 m 1 def 2 m 4 def 3 f 4 def 4 m 2 def 5 m 3 def |
The result from the first observation will be applied to the subsequent observations.