How to add a curve (smoothed line) to geom-bar in r?

for this data:

 big = runif(60);mangum = runif(61:120)
 df = data.frame(big, mangum)
 df_x <- eval(substitute(big), df)
 df_y <- eval(substitute(mangum), df)
 ccf.object <- ccf(df_x, df_y, plot = FALSE)
 output_table <- cbind(lag = ccf.object$lag, 
                    x.corr = ccf.object$acf) %>%
  as_tibble() %>%      mutate(cat = ifelse(x.corr > 0, "green", "red"))
 output_table %>%    ggplot(aes(x = lag, y = x.corr)) +
geom_bar(stat = "identity", aes(fill = cat))

[![enter image description here][1]][1]

How can add a smmothing curve above or below the bars like in the picture( bold line blue).

• geom_smooth() does not do what I need.

>Solution :

You could use stat_xspline from ggalt:

output_table %>%    
  ggplot(aes(x = lag, y = x.corr)) +
  geom_col(aes(fill = paste0(cat, 3), color = after_scale(alpha(fill, 1))), 
           alpha = 0.5) +
  geom_hline(yintercept = 0) +
  ggalt::stat_xspline(spline_shape = -0.5, color = 'blue', linewidth = 1) +
  scale_fill_identity() +
  theme_minimal()