df <- structure(list(`a a` = 1:3, `a b` = 2:4), .Names = c("a a", "a b"
), row.names = c(NA, -3L), class = "data.frame")
df <- structure(list(`a a` = 1:3, `a b` = 2:4),df <- structure(list(`a a` = 1:3, `a b` = 2:4), .Names = c("a a", "a b"
), row.names = c(NA, -3L), class = "data.frame")
df <- structure(list(`a a` = 1:3, `a b` = 2:4),