Saving charts

Standalone image file

The ggsave() function from ggplot2 can be used to save a standalone image file. To specify the SVG file format, simply ensure your file name ends with .svg. The following example uses the recommended dimensions from the previous section.

ggsave(myplot, filename = "example-plot.svg",
       width = 159, height = 100, units = "mm")

For a JPG or PNG image, also consider the DPI value. In ggsave, this can be supplied as a numerical value, or as a string input. For best quality, use “retina”.

ggsave(myplot, filename = "example-plot.png",
       width = 159, height = 100, units = "mm", dpi = "retina")

R Markdown

For charts in an R Markdown document, file format, dimensions and other settings can be set in the code chunk options.

• Format: Set dev = "svg", otherwise the default format of png will be used.

• Dimensions: Set fig.height and fig.width. For HTML outputs, the default figure dimensions are often suitable, however when knitting to Microsoft Word, the default dimensions often result in a small image and so it is best to specify these in the R Markdown code chunk. Note that R Markdown requires figure dimensions in inches. If you’d rather use millimetres, use the mm_to_inch helper function from afcharts.

• Alt Text: For HTML outputs, use fig.alt, and for Microsoft Word outputs, fig.cap. Note that by default, the value given to fig.cap will be shown under the chart. If you’d rather turn this off, you can control this in the R Markdown YAML header:

  output: 
    word_document:
     fig_caption: no

Set these options in a code chunk header:

```{r plot1, dev = "svg", fig.width = mm_to_inch(159), fig.height = mm_to_inch(100), fig.alt = "A description of plot1"}
plot1
```

It can sometimes make your code easier to read by specifying chunk options within the chunk:

```{r plot1}
#| dev = "svg"
#| fig.width = mm_to_inch(159)
#| fig.height = mm_to_inch(100)
#| fig.alt = "A description of plot1"

plot1
```

If you would like all of your images to be in the same format, it is usually easier to set options globally in the first code chunk of your document:

```{r setup, include = FALSE}
knitr::opts_chunk$set(
  dev = "svg",
  fig.width = mm_to_inch(159), 
  fig.height = mm_to_inch(100)
)
```

Note that afcharts must be loaded before setting global options, otherwise you will need to specify the package when calling mm_to_inch; e.g. afcharts::mm_to_inch().

There may be cases where you’d like all charts to be in SVG format, but with different dimensions. In this case you can set dev = "svg" in the global options and fig.width and fig.height for each code chunk separately.