Conditionally Display Block of Markdown Text Using Knitr

Conditionally display a block of text in R Markdown

You need a complete R expression, so you cannot break it into multiple blocks like you show, but if the results of a block are a text string then it will be included as is (without quotes), so you should be able to do something like:

`r if(show.text){"la la la"}`

and it will include the text if and only if show.text is TRUE.

Conditionally display block of markdown text using knitr

You could use the asis engine to conditionally include/exclude arbitrary text in knitr, e.g.

```{asis, echo=FALSE}
Some arbitrary text.

1. item
2. item

Change echo=TRUE or FALSE to display/hide this chunk.
```

But I just discovered a bug in this engine and fixed it. Unless you use knitr >= 1.11.6, you can create a simple asis engine by yourself, e.g.

```{r setup, include=FALSE}
library(knitr)
knit_engines$set(asis = function(options) {
  if (options$echo && options$eval) paste(options$code, collapse = '\n')
})
```

If you want to include inline R expressions in the text, you will have to knit the text, e.g.

```{r setup, include=FALSE}
library(knitr)
knit_engines$set(asis = function(options) {
  if (options$echo && options$eval) knit_child(text = options$code)
})
```

Conditionally display block of text with code inside string section

Using paste you could do:

Also note that there was a bug in your condition which I fixed.

---
title: "Untitled"
output: html_document
date: '2022-07-22'
---

```{r}
df <- data.frame(
  column = 1:2
)
```

`r if (nrow( subset(df,column == 1)) != 0) paste("Multiple choice variable with", nrow(subset(df, column == 1)), "missing values.") else ""`

Conditionally evaluate heading using knitr in .Rmd file

You can put the heading in an inline R expression:

```{r}
eval_cell = TRUE
```

`r if (eval_cell) '# Heading (would like to eval only if eval_cell is TRUE)'`

```{r eval = eval_cell}
summary(cars)
```

This will become cumbersome if you have large blocks of text/code that need to be conditionally included, in which case you are recommended to put them in a separate child document, say, child.Rmd:

# Heading (would like to eval only if eval_cell is TRUE)
```{r}
summary(cars)
```

Then in the original (parent) document, you just need

```{r}
eval_cell = TRUE
```

```{r child='child.Rmd', eval=eval_cell}
```

Display Block of R Code in Knitr With Evaluation Turned Off

Is this what you want to do, or have I misunderstood? The eval = FALSE is in one code chunk and the second chunk still plots.

---
title: "A Test Knit"
output: html_document
---

## Show code but don't run

```{r, eval = FALSE}
summary(cars)
```

## Run and render plot

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

quarto rmarkdown code block to only display certain lines

This does not work because you are using YAML syntax for chunk options as recommended with Quarto but #| echo: c(3) is not valid YAML. #| echo: 3 is.

You can use !expr within YAML field to parse R code if necessary. #| echo: !expr c(3) would work. It is explained here: https://quarto.org/docs/computations/r.html#chunk-options

However, know that knitr supports other way to specify chunk options:

• Usual header where option needs to be valid R code

```{r, echo = c(3)}
#| echo: c(3)
month <- "July"

str(month)
```

• And a multiline version of it, useful when having long option like fig.cap

```{r}
#| rmdworkflow,
#| echo = FALSE,
#| fig.cap = "A diagram illustrating how an R Markdown document
#|   is converted to the final output document.",
#| out.width = "100%"

knitr::include_graphics("images/workflow.png", dpi = NA)
```

See the announced in blog post for more about this new syntax: https://yihui.org/en/2022/01/knitr-news/

This question has also been asked in Github - so more detailed answer there: https://github.com/quarto-dev/quarto-cli/issues/863

Conditionally display markup formatted text based on shiny input

The the following in your Rmd file. You already are in a code block and don't need to have additional inline r formatting. You can use results = 'asis' in your block and also add the header (#) for identical formatting if you'd like:

```{r, echo=FALSE, results='asis'}
if(BoxValue == TRUE){
  cat("# Value for input 2 is", Input2Value)
}
```

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