如何在不创建新列的情况下递增数据框中的值？

df <- data.frame(a = c(1, 2, 3), b = c(4, 5, 6))

df <- apply(df, 2, function(x) {
  x <- seq(x[1], length.out = length(x), by = 1)
})

library(dplyr)

df <- data.frame(a = c(1, 2, 3), b = c(4, 5, 6))

df <- df %>% mutate(new_col = seq(a[1], length.out = n(), by = 1)) %>% transmute(new_col)

df <- data.frame(a = c(1, 2, 3), b = c(4, 5, 6))

for (i in 1:ncol(df)) {
  df[, i] <- seq(df[1, i], length.out = nrow(df), by = 1)
}