Stata 16 now integrates with Python. I’m pretty stoked about using some of the Python figure packages. Getting it up and running has been a bit of a challenge. Here’s how I got it to work.

Of note, since I started this post, Stata’s blog has started a series on using Python, which you should check out here.

Installing Anaconda (free for individuals, not for institutions)

Anaconda comes with many built-in statistical packages. The (free) individual version of Anaconda from here. Just make sure to check the “set as path” button during the Anaconda install!

Installing the (universally free) traditional Python distribution

As of July 2020, Python apparently has two versions that are commonly used, the 2.x version and the 3.x version. The end-of-life of 2.x versions is this year, so I wouldn’t recommend using it (current highest version is 2.7). Instead, use the 3.x version, currently the 3.8 version. You can find it at the Windows Python Download Page.

Make sure to install the version matching your Stata install! Stata comes as 32 bit or 64 bit. In Stata, type –about– to see what version you have. You’ll see that mine is running the 64-bit version of Stata. If you have a relatively modern computer, you are probably running the 64-bit version of Stata. Windows can actually run either 32-bit or 64-bit versions if you have a 64-bit processor, so do yourself a favor and just check. Type -about- in Stata to confirm your version.

Make sure that you install the corresponding version of Python. The highlighted one (x86-64) is the 64 bit. The other one (x86) is the 32-bit version. For this example, since I have the 64-bit version of stata, I installed the x86-64, 64-bit version of Python.

I had originally installed the 32-bit version of Python and Stata couldn’t load it. Installing the 64-bit version of Python solved that. There’s actually a big “download now” button on the main Python webpage that will give you the 32-bit version. Make sure to select the specific stable release in the picture above.

For the love of Pete, check this PATH box when you install it.

PATH is a list of commands that can be run from the Windows command line, and where their relative program exists.

See this check box right here? Select it. If you don’t, you’ll have a heck of a time getting anything to run from the command line. This should be checked on default, I have no idea why it’s not. If you forgot to check this box, uninstall Python and reinstall it after checking this box.

Also, notice that it says “64 bit” on the installer screen above. If it says “32 bit”, you probably downloaded the wrong version. Go back and try again!

What the heck did I just install?

There are two Python shell apps/programs that came along with the default Python setup. IDLE is a more user-friendly Python shell. It resembles the command line in Stata, but it has the syntax highlighting of the Do file editor.

The app called “Python 3.8 (64-bit)” is the shell without any markup. If you want to play around with Python, I recommend using IDLE.

Making your first program in IDLE

Anything you run in Python should be from a script, or a *.py file. Pop one open from within IDLE by hitting Ctrl+N. Enter the following:

print("Hello world!")

Then save it and run it (by pressing F5) and you’ll get the hello world!

How does that look in Stata?

Let’s do the same thing in a Stata do file. In order to open up the Python shell within Stata, you have to type –python– on its own line, your intended python code, then –end– on its own line. Here, I have entered:

python
print("hello world!")
end

Then just hit ctrl+d or the run button to get it to work in Stata!

How do I get the Pandas, Matplotlib, SciPy, Sklearn, and NumPy libraries installed?

Note: Anaconda comes with all of these except sklearn. For below, just complete the sklearn step.

Python by itself can do some stuff, but the heavy lifting for stats and visualization is from add-in libraries that aren’t included with the default Python and must be added in before doing much of anything else. (Note: Anaconda does come with those and is a Python installation geared towards science, but we’re doing the classic install here.) Installing these additional libraries can be done with the included pip library, which automates all downloads and installations. BUT pip it has to be called from the Windows command line, not in a Python shell (i.e., not in IDLE). You’ll know you’re in the shell if the line starts with this:

>>>

So if you type “pip install pandas” in the shell (after the “>>>”), you’ll get an error and you will not be getting pandas.

To pop up the Windows command line, hit the Start button then type “cmd” to open it up. Or hit windows key+r and type “cmd” to open it up. If you correctly checked the PATH checkbox in the install, you should get the version reported if you type the following in:

python --version

If you get some sort of error, it’s probably because you didn’t check the PATH box during the install. Uninstall Python then reinstall it and make for sure you check that stupid PATH box.

A note about the Windows 10 command line: If you type “Python” and hit enter, Windows pops up the Windows store and tries to get you to install the version of Python that they host. This is by far the dumbest Windows feature ever, and I have seen BOB. So, avoid ever typing the word “python” in the command line. Instead, use the handy “py” command, which does everything you’ll need it to do. Py is the python launcher.

To call pip, you want to type in “py” then “-m” then “pip” and its commands. the “-m” allows you to run library commands as a script. So, to install pandas, just type the following in to the command line:

py -m pip install pandas

You’ll see a screen like this:

…and ditto for the others (though it seems that NumPy installs along with pandas, it’s included here for completeness). When you are all done, you should have typed the following 5 lines individually:

py -m pip install pandas
py -m pip install matplotlib
py -m pip install numpy
py -m pip install scipy
py -m pip install sklearn

You only need to do this installation step once.

How do I use Pandas, Matplotlib, NumPy, Scikit-learn (sklearn), and SciPy in Stata?

Once the libraries are installed, you can then integrate them into your scripts. Each time you want to use them, you need to import them so you can call them. The convention is to import these using common so you don’t have to type “pandas” over and over again, you can just use “pd”. Ditto for other libraries:

python
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
import scipy as sp
import sklearn as sk
end

How do I install Jupyter Lab and get it to work with Stata? (This is the updated version of Jupyter Notebook)

Note: Jupyter lab comes installed with Anaconda, but node.js, npm, and stata_kernel still must be installed.

Jupyter is a super popular way to cleanly complete analyses. Its origins were in Python, but it now works in R and Stata. Details on installing Jupyter are here. Specific instructions for getting it to interface with Stata are here. Here’s how I got it installed:

First, install node.js. Download here. I checked the box in the node.js install to also install additional software. At the end of the install, it pops open Windows powershell window and installed a bunch of stuff, including Python, which is already installed. Perhaps it updated my Python version. It also installs Chocolatey and a few other things. Then, type the following in the Windows command line (if any of below doesn’t work, give your computer a reboot and try again):

pip install npm
pip install jupyterlab
pip install stata_kernel
py -m stata_kernel.install
jupyter labextension install jupyterlab-stata-highlight

Finally, you need to do a last step described here to get this to work in Windows. You can delete the new Stata desktop shortcut once you run it as an administrator one time.

Now you need to configure Jupyter to work with your Stata install. Details are here. I found the configuration file named .stata_kernel.conf sitting in this folder: C:\Users\MYUSERNAME\.stata_kernel.conf

In reviewing the configuration file, it seems to have correctly identified my Stata SE 16 setup. I changed the graph format from svg to png, but left the rest unchanged.

Now that I have Jupyter Lab installed, how do I open and use it?

In Anaconda Navigator, just click the “Jupyter lab” button. For a traditional Python install, open the Windows command line, type:

jupyter lab

It should open up your web browser to a Jupyter page. Keep the Windows Command line terminal open in the background. If you close it, Jupyter will cease to work. (Note: This isn’t true for anaconda if you open Jupyter from the GUI.) Click the “Stata” notebook button to start.

It’ll open up a scripting page for your code. At the bottom it should say “stata idle”. That’s how you know you set it up correctly.

Now you can use traditional Stata code!

There are additional programs called “Magics” detailed here that help Stata integrate more seamlessly with Jupyter. Each of these commands begins with a % symbol. There are specific ways to modify these commands.

• %browse – lists the first 200 rows
• %head – first 10 rows
• %tail – last 10 rows
• %set – can change the graph_format, graph_scale, graph_width, and graph_height

How do I use SFI to interface Stata and Python?

Stata and Python talk to each other using the Stata function interface, or SFI. MORE TO COME ON THIS.

I love restricted cubic splines, made famous by Frank Harrell (see his approach starting on page 58 here). Dr. Harrell made a package for automating these in R. I’m not aware of an equivalent package for Stata. Here’s my approach to making this specific restricted cubic spline in Stata.

The model here is modified Poisson regression using the Zou 2004 method since the outcome is binary. Since it’s coded as a GLM, it’ll be relatively easy to swap out this one specific model for other models, like logistic regression using the appropriate link & family. It’s good habit to have the probability density of the outcome across the continuum of exposure, so that is plopped on the bottom here. It wouldn’t take much work to replace with a histogram.

This is for two groups (group1=blue, group2=red). It wouldn’t be too hard to make this for just one group, deleting everything having to do with group 2 or having the number 2 in it. Or, duplicate lines for a group 3. Also, sometimes folks like to present a kernel density plot for each outcome, so you’d just duplicate the kdensity lines and add some code to specify that one of each is for folks with outcome==0 then outcome==1.

One quirk is that the xbrcspline code depends on a list of all of the possible options for the exposure, which is brought in from listof to xbrcspline as a numlist. As you can see in –help limits–, numlists are capped at 2,500 numbers. If you get an error saying “values() invalid — invalid numlist has too many elements”, then you have too many individual options for your exposure. This might be because your exposure is an integer with a huge amount of digits after the decimal place, so your >2,500 observations all come with their own unique value for the exposure. Rounding can help reduce this count, if it analytically and clinically makes sense. (This is okay for BMI, for example, because there isn’t clinically relevant difference between a bmi of 27.0400558235 and 27.04). To generate a rounded value, plop —gen bmi_round=(bmi, 0.01)– in the first few lines, right after opening your data. Then use “bmi_round” as your exposure variable rather than “bmi”.

This code is an essentially entirely rewritten version of one that is used at the Welch Center at Hopkins, where it has been handed down through generations of doctoral students and post-docs.

I’ve recently needed to make these figures using pweights, so I put some comments throughout to simplify that process.

Enjoy!

Code to make the figure above

*************************************************
***************load data!************************
****************and drop any open graphs*********
*************************************************
webuse fvex, clear
graph drop _all
macro drop _all
// if weighted, declare weighting here
*************************************************
**************define variables here**************
*************************************************
// Define the OUTCOME, = to 0 or 1, after the (first) word "outcome"
global outcome outcome // this database's outcome is called outcome...
// Define the EXPOSURE following the word "exposure"
global exposure age // this has to be a continuous variable
// Define the COVARIATES following word "covariate"
global covariates sex distance
// Define what makes GROUP 1 here after "thing1" (blue)
global thing1 if arm==1 
// Define what makes GROUP 2 here after "thing2" (red)
global thing2 if arm==2

*************************************************
************auto-generate subgroups and**********
*****************local macros needed*************
********************for spline*******************
*************************************************
// need to make the exposure by group for the kernel density plots. 
gen exposuresubgroup1 = ${exposure} ${thing1}
gen exposuresubgroup2 = ${exposure} ${thing2}

// The xbrcspine command below needs the middle value of the exposure 
// for each group. This is often times the median, but if there are 
// an even number of values for the exposure, the median will be an 
// average of the two middle values of the exposure variable. The following 
// code defines the median as a local macro (median1temp) then grabs the
// actual value for the exposure closest to that number (median_1). 
// _pctile can be used with pweight, if needed.
//
_pctile ${exposure} ${thing1}, p(50)
local median1temp = r(r1)
gen mediandiff1=abs(exposuresubgroup1-`median1temp')
gsort mediandiff1
local median_1 = ${exposure}[_n==1]
//
_pctile ${exposure} ${thing2}, p(50)
local median2temp = r(r1)
gen mediandiff2=abs(exposuresubgroup2-`median2temp')
gsort mediandiff2
local median_2 = ${exposure}[_n==1]
//
// get rid of these variables, since they are not needed anymore
drop mediandiff1 mediandiff2

*************************************************
*************make splines and view knots!********
*************************************************
// NOTE: look at the stata output here, the knots will be displayed
// you'll need to list these in the footer
// 
// Harrell's method recommends using the # of knots ('k') as 3, 4 or 5
// with n >=100 as 5 and n<30 as 3. It's just a guideline. 
// Details are on page 62 here: 
// http://biostat.mc.vanderbilt.edu/wiki/pub/Main/BioMod/notes.pdf
mkspline ${exposure}_spline1=${exposure} ${thing1}, nknots(4) cubic displayknots
mat knots1=r(knots)
mkspline ${exposure}_spline2=${exposure} ${thing2}, nknots(4) cubic displayknots
mat knots2=r(knots)
// above won't work for pweight weighted data. instead, you need 
// to specifically define the percentiles from the table on pg 5 here:
// https://www.stata.com/manuals13/rmkspline.pdf
// But basically, 
// 3 knots, percentiles are at: 10 50 90
// 4 knots, percentiles are at: 5 35 65 95
// 5 knots, percentiles are at: 5 27.5 50 72.5 95
// 6 knots, percentiles are at: 5 23 41 59 77 95
// 7 knots, percentiles are at: 2.5 18.33 34.17 50 65.83 81.67 97.5
// the code for 4 knots follows in hidden code:
//
//_pctile ${exposure} ${thing1} [pweight=samplingweight], p(5 35 65 95) 
//return list
//local gr1knot1 = r(r1)
//local gr1knot2 = r(r2)
//local gr1knot3 = r(r3)
//local gr1knot4 = r(r4)
//di "Knots for group 1 are at " `gr1knot1' ", " `gr1knot2' ", " ///
//`gr1knot3' ", " `gr1knot4' "."
//
//
//mkspline ${exposure}_spline1=${exposure} ${thing1},  ///
//knots(`gr1knot1' `gr1knot2' `gr1knot3' `gr1knot4' ) ///
//cubic displayknots
//
//mat knots1=r(knots)
//
//_pctile ${exposure} ${thing2} [pweight=samplingweight], p(5 35 65 95) 
//return list
//local gr2knot1 = r(r1)
//local gr2knot2 = r(r2)
//local gr2knot3 = r(r3)
//local gr2knot4 = r(r4)
//
//di "Knots for group 2 are at " `gr2knot1' ", " `gr2knot2' ", " ///
// `gr2knot3' ", " `gr2knot4' "."
//
//
//mkspline ${exposure}_spline2=${exposure} ${thing2},  ///
//knots(`gr2knot1' `gr2knot2' `gr2knot3' `gr2knot4') ///
//cubic displayknots
//
//mat knots2=r(knots)
*************************************************
********Generate models to use in splines********
*************************************************
// model time!
// the models here are modified poisson regressions using sandwich variance estimators
// which is the Zou method from this classic paper:
// https://pubmed.ncbi.nlm.nih.gov/15033648/
// GLMs can be used with pweight, if needed.
//
// First group 
glm ${outcome} c.${exposure}_spline1* ${covariates}  ${thing1},  ///
fam(poisson) link(log) nolog robust
// robust is required for modified poisson regression by zou's method 
// (i.e., modified poisson regression with sandwich variance estimators)
levelsof(${exposure})  ${thing1}  // generates r(levels) for next line
xbrcspline ${exposure}_spline1, values(`r(levels)') ///
ref(`median_1') matknots(knots1) /// 
eform gen(lpnt1 hr1 lb1 ub1)

// Second group
glm ${outcome} c.${exposure}_spline2* ${covariates} ${thing2}, ///
fam(poisson) link(log) nolog robust
///
levelsof(${exposure}) ${thing2} // generates r(levels) for next line
xbrcspline ${exposure}_spline2, values(`r(levels)') ///
ref(`median_2') matknots(knots2) /// 
eform gen(lpnt2 hr2 lb2 ub2)

*************************************************
***********generate extremes to drop*************
*************************************************
// should drop the extremes, here the 0.5 and 99.5th percentiles
// but need to define these as local macros.
// _pctile can be used with pweight, if needed.
_pctile ${exposure} ${thing1}, p(0.05 99.5)
return list
local cut_a1 = r(r1)
local cut_b1 = r(r2)

_pctile ${exposure} ${thing2}, p(0.05 99.5)
return list
local cut_a2 = r(r1)
local cut_b2 = r(r2)

*************************************************
***************make the figure*******************
*************************************************
set scheme s1mono // my favorite scheme
twoway ///
/// spline for one group
(line  hr1 lpnt1 if lpnt1 > `cut_a1' & ///
lpnt1 < `cut_b1' , yaxis(1) lp(solid) lc(blue) lwidth(medthick) ) ///

(rarea lb1 ub1 lpnt1 if lpnt1 > `cut_a1' & ///
lpnt1 < `cut_b1' , yaxis(1) color(blue%5)) ///

(line  lb1 lpnt1 if lpnt1 > `cut_a1' & ///
lpnt1 < `cut_b1', yaxis(1)  lp(dash) lc(blue) lwidth(thin) ) ///

(line  ub1 lpnt1 if lpnt1 > `cut_a1' & ///
lpnt1 < `cut_b1' , yaxis(1) lp(dash) lc(blue) lwidth(thin) ) ///

/// spline for other group
(line  hr2 lpnt2 if lpnt2 > `cut_a2' & ///
lpnt2 < `cut_b2' , yaxis(1) lp(solid) lc(red) lwidth(medthick) ) ///

(rarea lb2 ub2 lpnt2 if lpnt2 > `cut_a2' & ///
lpnt2 < `cut_b2' , yaxis(1) color(red%5)) ///

(line  lb2 lpnt2 if lpnt2 > `cut_a2' & ///
lpnt2 < `cut_b2' , yaxis(1)  lp(dash) lc(red) lwidth(thin) ) ///

(line  ub2 lpnt2 if lpnt2 > `cut_a2' & ///
lpnt2 < `cut_b2' , yaxis(1) lp(dash) lc(red) lwidth(thin) ) ///

(line  ub2 lpnt2 if lpnt2 > `cut_a2' & ///
lpnt2 < `cut_b2' , yaxis(1) lp(dash) lc(red) lwidth(thin) ) ///

/// kernel density for one group
(kdensity exposuresubgroup1 if exposuresubgroup1 > `cut_a1' & ///
exposuresubgroup1 < `cut_b1' , yaxis(2) lp(shortdash) lcolor(blue)) ///

/// kernel density for other group
(kdensity exposuresubgroup2 if exposuresubgroup2 > `cut_a2' & ///
exposuresubgroup2 < `cut_b2' , yaxis(2) lp(shortdash) lcolor(red)) ///

, ///
yline(1, lpattern(solid) lcolor(black) axis(1)) ///
/// labels for the left axis, hide the following line if you aren't sure 
/// of what the range should be:
ylabel(0.25 "0.25" 0.5 "0.5" 1 "1" 2.5 "2.5" 5 "5", axis(1) angle(0)) ///
/// range for the left axis. the BOTTOM of this range has to be WAAAY lower 
/// than the bottom ylabel in the line above in order for it to sit 
/// on the way top of the figure. 
yscale(r(0.001 2) log axis(1)) /// log scale here
/// ditto for the right axis, but the TOP of the range on the yscale needs 
/// to be WAAAY higher than the top ylabel
ylabel(0 "0" 0.01 "0.01" 0.02 "0.02" 0.03 "0.03" 0.04 "0.04" 0.05 "0.05", ///
axis(2) labsize(vsmall) angle(0)) ///
yscale(r(0.0 .2) axis(2)) /// not log scale here
/// you'll notice that the x label doesn't span the entire 
/// range of the exposure because the local macro cuts above.
xlabel(20(5)60) ///
/// for the titles, need to put a bunch of spaces so things align
ytitle("                {bf:Risk Ratio (95% CI)}", axis(1)) ///
ytitle("{bf:Probability Density}                                          ", ///
 justification(left) axis(2)) ///
xtitle("{bf:Exposure Here}") ///
title("{bf:The Title}") ///
legend(order(1 "Group 1" 5 "Group 2")) ///
name(mygraph1)
			
*************************************************
*****************Save figure!********************
*************************************************
// save as png, change to tif if needed for submission			
graph export "mygraph1.png", replace width(1000)