---
title: Modern Spreadsheets in Stata
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[Stata](https://www.stata.com/) is a statistical software package. It offers a
robust C-based extension system.
[SheetJS](https://sheetjs.com) is a JavaScript library for reading and writing
data from spreadsheets.
This demo uses SheetJS to pull data from a spreadsheet for further analysis
within Stata. We'll create a Stata native extension that loads the
[Duktape](/docs/demos/engines/duktape) JavaScript engine and uses the SheetJS
library to read data from spreadsheets and converts to a Stata-friendly format.
```mermaid
flowchart LR
ofile[(workbook\nXLSB file)]
nfile[(clean file\nXLSX)]
data[[Stata\nVariables]]
ofile --> |Stata Extension\nSheetJS + Duktape| nfile
nfile --> |Stata command\nimport excel|data
```
The demo will read [a Numbers workbook](https://sheetjs.com/pres.numbers) and
generate variables for each column. A sample Stata session is shown below:
:::info pass
This demo covers Stata extensions. For directly processing Stata DTA files, the
["Stata DTA Codec"](/docs/constellation/dta) works in the browser or NodeJS.
:::
:::note Tested Deployments
This demo was tested by SheetJS users in the following deployments:
| Architecture | Date |
|:-------------|:-----------|
| `darwin-x64` | 2024-04-10 |
| `win10-x64` | 2024-04-10 |
:::
:::info pass
Stata has limited support for processing spreadsheets through the `import excel`
command[^1]. At the time of writing, it lacked support for XLSB, NUMBERS, and
other common spreadsheet formats.
SheetJS libraries help fill the gap by normalizing spreadsheets to a form that
Stata can understand.
:::
## Integration Details
The current recommendation involves a native plugin that reads arbitrary files
and generates clean XLSX files that Stata can import.
The extension function ultimately pairs the SheetJS `read`[^2] and `write`[^3]
methods to read data from the old file and write a new file:
```js
var wb = XLSX.read(original_file_data, {type: "buffer"});
var new_file_data = XLSX.write(wb, {type: "array", bookType: "xlsx"});
```
The extension function `cleanfile` will take one or two arguments:
`plugin call cleanfile, "pres.numbers"` will generate `sheetjs.tmp.xlsx` from
the first argument (`"pres.numbers"`) and print instructions to load the file.
`plugin call cleanfile, "pres.numbers" verbose` will additionally print CSV
contents of each worksheet in the workbook.
```mermaid
flowchart LR
ofile{{File\nName}}
subgraph JS Operations
ojbuf[(Buffer\nFile Bytes)]
wb(((SheetJS\nWorkbook)))
njbuf[(Buffer\nXLSX bytes)]
end
obuf[(File\nbytes)]
nbuf[(New file\nbytes)]
nfile[(XLSX\nFile)]
ofile --> |C\nRead File| obuf
obuf --> |Duktape\nBuffer Ops| ojbuf
ojbuf --> |SheetJS\n`read`| wb
wb --> |SheetJS\n`write`| njbuf
njbuf --> |Duktape\nBuffer Ops| nbuf
nbuf --> |C\nWrite File| nfile
```
### C Extensions
Stata C extensions are shared libraries or DLLs that use special Stata methods
for parsing arguments and returning values.
#### Structure
Arguments are passed to the `stata_call` function in the plugin.[^4] The
function receives the argument count and an array of C strings:
```c title="stata_call declaration"
STDLL stata_call(int argc, char *argv[]);
```
For example, `argc` is 2 and `argv` has two C strings in the following command:
```stata
plugin call cleanfile, "pres.numbers" verbose
* arguments start
* argv[0] ^^^^^^^^^^^^
* argv[1] ^^^^^^^
* argc = 2
```
#### Communication
`SF_display` and `SF_error` display text and error messages respectively.
Message text follows the "Stata Markup and Control Language"[^5].
`{stata ...}` is a special directive that displays the arguments and creates a
clickable link. Clicking the link will run the string.
For example, a plugin may attempt to print a link:
```c title="SF_display C plugin example"
SF_display("{stata import excel \"sheetjs.tmp.xlsx\", firstrow} will read the first sheet and use headers\n");
```
The function will print the following text to the terminal:
import excel "sheetjs.tmp.xlsx", firstrow will read the first sheet and use headers
The blue text is clickable. When a user clicks the text, the command
`import excel "sheetjs.tmp.xlsx", firstrow` will be executed.
### Duktape JS Engine
This demo uses the [Duktape JavaScript engine](/docs/demos/engines/duktape). The
SheetJS + Duktape demo covers engine integration details in more detail.
The [SheetJS Standalone scripts](/docs/getting-started/installation/standalone)
can be loaded in Duktape by reading the source from the filesystem.
## Complete Demo
:::info pass
This demo was tested in Windows x64 and macOS x64. The path names and build
commands will differ in other platforms and operating systems.
:::
The [`cleanfile.c`](pathname:///stata/cleanfile.c) extension defines one plugin
function. It can be chained with `import excel`:
```stata
program cleanfile, plugin
plugin call cleanfile, "pres.numbers" verbose
program drop cleanfile
import excel "sheetjs.tmp.xlsx", firstrow
```
### Create Plugin
0) Ensure a compatible C compiler (Xcode on macOS) is installed.
1) Open Stata and run the following command:
```stata
pwd
```
The output will be the default data directory. On macOS this is typically
`~/Documents/Stata`
2) Open a terminal window and create a project folder `sheetjs-stata` within the
Stata data directory:
```bash
# `cd` to the Stata data directory
cd ~/Documents/Stata
mkdir sheetjs-stata
cd sheetjs-stata
```
0) Ensure "Windows Subsystem for Linux" (WSL) and Visual Studio are installed.
1) Open a new "x64 Native Tools Command Prompt" window and create a project
folder `c:\sheetjs-stata`:
```powershell
cd c:\
mkdir sheetjs-stata
cd sheetjs-stata
```
2) Enter WSL:
```powershell
bash
```
3) Download [`stplugin.c`](https://www.stata.com/plugins/stplugin.c) and
[`stplugin.h`](https://www.stata.com/plugins/stplugin.h) from the Stata website:
```bash
curl -LO https://www.stata.com/plugins/stplugin.c
curl -LO https://www.stata.com/plugins/stplugin.h
```
4) Download Duktape. In Windows, the following commands should be run in WSL. In
macOS, the commands should be run in the same Terminal session.
```bash
curl -LO https://duktape.org/duktape-2.7.0.tar.xz
tar -xJf duktape-2.7.0.tar.xz
mv duktape-2.7.0/src/*.{c,h} .
```
5) Download [`cleanfile.c`](https://docs.sheetjs.com/stata/cleanfile.c).
In Windows, the following commands should be run in WSL. In macOS, the commands
should be run in the same Terminal session.
```bash
curl -LO https://docs.sheetjs.com/stata/cleanfile.c
```
6) Observe that macOS does not need a "Linux Subsystem" and move to Step 7.
7) Build the plugin:
```bash
gcc -shared -fPIC -DSYSTEM=APPLEMAC stplugin.c duktape.c cleanfile.c -lm -std=c99 -Wall -ocleanfile.plugin
```
6) Exit WSL:
```bash
exit
```
The window will return to the command prompt.
7) Build the DLL:
```powershell
cl /LD cleanfile.c stplugin.c duktape.c
```
### Install Plugin
8) Copy the plugin to the Stata data directory:
```bash
cp cleanfile.plugin ../
```
8) Copy the DLL to `cleanfile.plugin` in the Stata data directory. For example,
with a shared data directory `c:\data`:
```powershell
mkdir c:\data
copy cleanfile.dll c:\data\cleanfile.plugin
```
### Download SheetJS Scripts
9) Move to the Stata data directory:
```bash
cd ..
```
10) Observe that macOS does not need a "Linux Subsystem" and move to Step 11.
9) Move to the `c:\data` directory:
```powershell
cd c:\data
```
10) Enter WSL
```powershell
bash
```
11) Download SheetJS scripts and the test file.
In Windows, the following commands should be run in WSL. In macOS, the commands
should be run in the same Terminal session.
{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers`}
### Stata Test
:::note pass
The screenshot in the introduction shows the result of steps 13 - 19
:::
12) If it is not currently running, start the Stata application.
13) Run the following command in Stata:
```stata
dir
```
Inspect the output and confirm that `cleanfile.plugin` is listed.
13) Move to the `c:\data` directory in Stata:
```stata
cd c:\data
```
14) Load the `cleanfile` plugin:
```stata
program cleanfile, plugin
```
16) Read the `pres.numbers` test file:
```stata
plugin call cleanfile, "pres.numbers" verbose
```
The result will show the data from `pres.numbers`:
. plugin call cleanfile, "pres.numbers" verbose
Worksheet 0 Name: Sheet1
Name,Index
Bill Clinton,42
GeorgeW Bush,43
Barack Obama,44
Donald Trump,45
Joseph Biden,46
Saved to `sheetjs.tmp.xlsx`
import excel "sheetjs.tmp.xlsx", firstrow will read the first sheet and use headers
for more help, see import excel
17) Close the plugin:
```stata
program drop cleanfile
```
18) Clear the current session:
```stata
clear
```
In the result of Step 16, click the link on import
excel "sheetjs.tmp.xlsx", firstrow
Alternatively, manually type the command:
```stata
import excel "sheetjs.tmp.xlsx", firstrow
```
The output will show the import result:
. import excel "sheetjs.tmp.xlsx", firstrow
(2 vars, 5 obs)
20) Open the Data Editor (in Browse or Edit mode) and compare to the screenshot:
```stata
browse Name Index
```
[^1]: Run `help import excel` in Stata or see ["import excel"](https://www.stata.com/manuals/dimportexcel.pdf) in the Stata documentation.
[^2]: See [`read` in "Reading Files"](/docs/api/parse-options)
[^3]: See [`write` in "Writing Files"](/docs/api/write-options)
[^4]: See ["Creating and using Stata plugins"](https://www.stata.com/plugins/#sect8) in the Stata website
[^5]: run `help smcl` in Stata or see ["smcl"](https://www.stata.com/manuals/psmcl.pdf) in the Stata documentation.