How to delay chunk echo and easily print all code at the end using knitr

delay_code.Rmd

---
title: "Untitled"
author: "Michael C Sachs"
date: "24 augusti 2016"
output: html_document
---

```{r setup, include=FALSE}
library(knitr)

delay_code_labels <- NULL

knit_hooks$set(delay = function(before, options, envir) {
    if (before) {
        delay_code_labels <<- append(delay_code_labels, options$label)
        return(NULL)  ## otherwise knitr will print delay_code_labels every time
    } else {
        
    }
})

opts_chunk$set(delay = TRUE, echo = FALSE, message = FALSE, warning = FALSE, 
               fig.width = 6, fig.asp = 0.618)
```

## R Markdown

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r norm}
rnorm(10)
```

```{r cars}
summary(cars)
```

## Including Plots

You can also embed plots, for example:

```{r pressure}
plot(pressure)
```

## Appendix

### Code


```{r codeprint, echo = TRUE, eval = FALSE, ref.label = delay_code_labels, delay = FALSE}
```

```{r}
sessionInfo()
```

very useful! thanks