girls.R

library(tidyverse)
library(scales)

# bc who column names are weird
parse_percentile <- function(x){
  x <- str_replace( x, "^P", "" )
  case_when( 
    x == "01"  ~ .1,
    x == "999" ~ 99.9,
    TRUE       ~ as.numeric(x) 
  )
}

url <- "http://www.who.int/childgrowth/standards/wfa_girls_p_exp.txt"
baby_girls_weight <- read_delim(url, delim = "\t" ) %>% 
  select( -(L:S) ) %>% 
  gather( percentile, weight, -Age) %>% 
  mutate( percentile = parse_percentile(percentile) )

scale_color_gradient_mirror <- function (..., colors ,  
  midpoint = 0, space = "Lab", na.value = "grey50", guide = "colourbar") {
  cols <- c( head(colors, -1), tail( colors, 1), rev( head( colors, -1)) )
  continuous_scale("colour", "gradient2", 
    gradient_n_pal( cols ), 
    na.value = na.value, guide = guide, 
    ..., rescaler = ggplot2:::mid_rescaler(mid = midpoint))
}

ggplot( filter(baby_girls_weight, Age < 100) ) +
  scale_color_gradient_mirror(midpoint=50, colors = c("pink", "purple", "blue") ) +
  aes( Age, weight, color = percentile, group = percentile ) +
  geom_line( ) + 
  xlab( "Days" ) + 
  ylab( "Weight (kg)") + 
  theme_light() +
  geom_text( 
    data = filter(baby_girls_weight, Age == 100), 
    mapping  = aes( Age + 2 , weight, label = percentile, color = NULL ), 
    size = 2
  ) + 
  geom_text( 
    data = filter(baby_girls_weight, Age == 0), 
    mapping  = aes( Age - 2 , weight, label = percentile, color = NULL ), 
    size = 2
  ) +
  guides(colour=FALSE)