Non-standard evaluation (NSE) in dplyr’s filter_ & pulling data from MySQL

Question

It’s not really related to SQL. This example in R does not work either:

df <- data.frame(
     v1 = sample(5, 10, replace = TRUE),
     v2 = sample(5,10, replace = TRUE)
)
df %>% filter_(~ "v1" == 1)

It does not work because you need to pass to filter_ the expression ~ v1 == 1 — not the expression ~ "v1" == 1.

To solve the problem, simply use the quoting operator quo and the dequoting operator !!

library(dplyr)
which_column = quot(v1)
df %>% filter(!!which_column == 1)