Let us consider an example where we study the mpg and weight variables in auto.dta. In our examples below, we will first write the commands so that they will be displayed in our target HTML file. Then, we will write the commands so that Stata will process the Stata dynamic tags, displaying the results of the Stata commands in the target HTML file.
We first use the sysuse command to load the dataset and then describe the data using the describe command.
<<dd_do>>
sysuse auto, clear
describe
<</dd_do>>
This produces the following Stata results:
. sysuse auto, clear
(1978 automobile data)
. describe
Contains data from /usr/local/stata18/ado/base/a/auto.dta
Observations: 74 1978 automobile data
Variables: 12 13 Apr 2022 17:45
(_dta has notes)
-------------------------------------------------------------------------------
Variable Storage Display Value
name type format label Variable label
-------------------------------------------------------------------------------
make str18 %-18s Make and model
price int %8.0gc Price
mpg int %8.0g Mileage (mpg)
rep78 int %8.0g Repair record 1978
headroom float %6.1f Headroom (in.)
trunk int %8.0g Trunk space (cu. ft.)
weight int %8.0gc Weight (lbs.)
length int %8.0g Length (in.)
turn int %8.0g Turn circle (ft.)
displacement int %8.0g Displacement (cu. in.)
gear_ratio float %6.2f Gear ratio
foreign byte %8.0g origin Car origin
-------------------------------------------------------------------------------
Sorted by: foreign
Now, we want to check if mpg is always greater than 0 and less than 100. We use the assert command to perform the check. In this case, we do not want to include any output in the target HTML file, so we use the quietly attribute to modify the behavior of the dd_do Stata dynamic tag.
<<dd_do:quietly>>
assert mpg > 0 & mpg < 100
<</dd_do>>
If the data do not satisfy the conditions, dyndoc will fail with an error message, which will occur if we run the same assert command in a do-file.
Next, we want to summarize the weight variable:
<<dd_do>>
summarize weight
<</dd_do>>
This produces the following in the target HTML file:
. summarize weight
Variable | Obs Mean Std. dev. Min Max
-------------+---------------------------------------------------------
weight | 74 3019.459 777.1936 1760 4840
We want to use the minimum and maximum values of weight in a sentence. Instead of copying and pasting the numbers from the summarize output, we can use the dd_display Stata dynamic tag with the r(min) and r(max) stored results:
The variable weight has minimum value <<dd_display: %4.2f `r(min)'>> and
has maximum value <<dd_display: %4.2f `r(max)'>>.
This produces the following in the target HTML file:
> The variable weight has minimum value 1760.00
and has maximum value 4840.00.
The dd_display dynamic tag uses the display command to evaluate expressions. It can be used as a calculator. For example, if we want to include the $$range = max - min$$ in a sentence, instead of calculating the number and then copying and pasting it, we can use
The variable weight has range <<dd_display: %4.2f `r(max)'-`r(min)'>>.
which produces the following in the target HTML file:
> The variable weight has range 3080.00.
Now, we want to graph mpg and weight using a scatterplot. We use the dd_do tag with the nooutput attribute to generate the scatterplot first. The nooutput attribute leaves the command in the output only,
<<dd_do:nooutput>>
scatter mpg weight, mcolor(blue%50)
<</dd_do>>
which generates a scatterplot of mpg and weight with 50% opacity color markers.
. scatter mpg weight, mcolor(blue%50)
Now, we want to export the graph to a file and include an image link to the file.
<<dd_graph: sav("graph.svg") alt("scatter mpg weight") replace height(400)>>
This produces a graph of 400 pixels high.