title: Create multiple plots with unique RMarkdown headers
body: <p>Using <code>spineplot</code> in R, I am trying to create a series of plots that compare some potential covariates against age categories so we can do some preliminary data exploration. I have this code written up in R Markdown and I am using RStudio to knit the file into an HTML output. However, I am having difficulty getting each plot produced by my loop to have an appropriate RMarkdown header. I have tried putting <code>cat("## my header")</code> in the loop that produces each plot, but for some reason it only shows up for the first plot, and not the rest. It <em>prints out</em> for the rest of them, but does not get interpreted as Markdown.</p>
  
  <p>Here's an example of my code:</p>
  
  <pre><code>---
  title: "Minimal Working Example"
  author: "TARehman"
  date: "Wednesday, August 27, 2014"
  output:
    html_document:
      toc: yes
  ---
  
  # Spineplots
  ```{r mwe, echo=FALSE, results='asis', fig.height=5, fig.width=8, dpi=300}
  tempdata &lt;- data.frame(age=c("0-1","0-1","1-3","1-3","3-7","10-15","3-7","7-10"),
                         covA=c("Class 0","Class 1","Class 3","Class 2","Class 4","Class 3","Class 1","Class 2"),
                         covB=c("Class 1","Class 3","Class 2","Class 4","Class 4","Class 1","Class 1","Class 0"),
                         covC=c("Class 3","Class 3","Class 2","Class 3","Class 1","Class 4","Class 4","Class 4"))
  
  temp_covars &lt;- c("covA","covB","covC")
  
  temp_locvec &lt;- c(0.1,0.3,0.5,0.7,0.9)
  temp_labvec &lt;- c("0-1","1-3","3-7","7-10","10-15")
  temp_colvec &lt;- rainbow(n = 5,start = 7/12,end = 9/12,alpha = 0.8)
  
  for(x in temp_covars) {
  
      cat(paste("## Spineplot of",x,"vs. age groups\n",sep=" "))
  
      spineplot(x = tempdata[[x]],
                y = tempdata$age,
                ylab = "Age Group",
                xlab = "Class",
                col = temp_colvec,
                off = 0,
                yaxlabels = c(NA,NA,NA,NA,NA),
                main = paste("Classes of",x,"versus age groups",sep=" "))
  
      for(j in 1:5) {
          axis(side = 2,
               at = temp_locvec[j],
               labels = temp_labvec[j],
               col.axis = temp_colvec[j],
               font.axis = 2)
          }
      rm(j)
  }
  rm(list=c("x","temp_locvec","temp_labvec","temp_colvec"))
  ```
  </code></pre>
  
  <p>The output looks like this.</p>
  
  <p><img src="https://i.stack.imgur.com/R9tla.png" alt="Minimal Working Example Output"></p>