5 Linking Code Blocks
5.1 Linking Code Blocks
Most documents have alternating blocks of code, output, and explanatory text. And very often the code illustrated in later blocks will depend in some way on code in the previous blocks. However, each code block (also called a "code chunk") is executed as a separate Stata session.
For example, your first block of code might load a data set, calculate a new variable, and provide summary statistics (see below). You then provide some explanatory text that tells the reader about the analysis you are about to do, followed by the code block for the analysis and the output. Because the second, "analysis" code block is executed as a separate Stata session, you have to reload the data set and re-calculate the new variable.
One way to have some "setup" code execute silently at the start of each Stata code block is to put it in a file named profile.do, located in the same folder as your Markdown file. (See the Stata FAQ about profile.do files: Stata looks for this file every time it starts up.)
Statamarkdown provides a chunk option to collect your code
as you go,
and adds each block of code to your profile.do.
You may not want all of your code to end up in the profile.do, so the implementation here makes it a user-specified option whether or not each code block is added to the profile.do. For longer documents, try to collect as little code as possible, or it will really slow down the generation of your document!
5.2 Locals, Scalars, and Globals
Note that local macros defined in profile.do disappear after the profile has run. In other words, you cannot accumulate local macro definitions across code blocks. Instead, you should use Stata’s scalars or global macros.
5.3 An Example
This illustrates what we would like to be able to do.
A first code block:
(1978 automobile data)
Variable | Obs Mean Std. dev. Min Max
-------------+---------------------------------------------------------
price | 74 6165.257 2949.496 3291 15906
gpm | 74 .0501928 .0127986 .0243902 .0833333A second, later code block:
Source | SS df MS Number of obs = 74
-------------+---------------------------------- F(1, 72) = 35.95
Model | 211486574 1 211486574 Prob > F = 0.0000
Residual | 423578822 72 5883039.19 R-squared = 0.3330
-------------+---------------------------------- Adj R-squared = 0.3238
Total | 635065396 73 8699525.97 Root MSE = 2425.5
------------------------------------------------------------------------------
price | Coefficient Std. err. t P>|t| [95% conf. interval]
-------------+----------------------------------------------------------------
gpm | 132990 22180.86 6.00 0.000 88773.24 177206.7
_cons | -509.8827 1148.469 -0.44 0.658 -2799.314 1779.548
------------------------------------------------------------------------------5.4 The collectcode Chunk Option
The implementation here makes use of a "chunk hook", collectcode.
With the Statamarkdown library loaded, this option
is available for any Stata code chunk.
In the example (above), I added code from the first Stata chunk (labelled "first-Stata") to the profile.do, but not code from the second chunk.
A first code block:
```{stata first-Stata, collectcode=TRUE}
sysuse auto
generate gpm = 1/mpg
summarize price gpm
```
A second, later code block:
```{stata second-Stata}
regress price gpm
```