Combine leaflet and markdown in loop - knitr

Question

This question shows how to loop over/apply leaflet objects within a markdown file. I'd like to do a similar thing, though I'd like to add additional markdown content.
---
title: "Test"
output: html_document
---
```{r setup, echo=T,results='asis'}
library(leaflet)
library(dplyr) ### !!! uses development version with tidyeval !!!
library(htmltools)
##Add A Random Year Column
data(quakes)
quakes <- tbl_df(quakes) %>%
mutate(year = sample(2008:2010, n(), replace=TRUE))
```
```{r maps, echo=T,results='asis'}
createMaps <- function(year){
cat(paste("###", year, "\n"))
leaflet(quakes %>% filter(year == !!year)) %>%
addTiles() %>%
addMarkers(
lng = ~long,
lat = ~lat,
popup = ~as.character(mag))
cat("\n\n")
}
htmltools::tagList(lapply(as.list(2008:2010), function(x) createMaps(x) ))
```
If I leave out the cat statements in the createMaps function, this code prints all three maps. If I put in the cat statements, I get the markdown, but no maps. Any way to combine both types of element?

Answer 1

The problem is, that your cat statements are being evaluated, before lapply returns its result list.
Delete the cat statements, change your createMaps function to
createMaps <- function(year){
mymap <- leaflet(quakes %>% filter(year == !!year)) %>%
addTiles() %>%
addMarkers(
lng = ~long,
lat = ~lat,
popup = ~as.character(mag))
return(list(tags$h1(year), mymap))
}
and change tags$h1() to whatever size of header you want (tags$h2(), ...)