Data Management
2026-04-0413 min read

keep/drop in Stata: Subset Data Without Accidental Loss

Use keep drop stata in Stata with full runnable code, realistic panel variables, and QA checks before downstream estimation.

Sytra Team
Research Engineering Team, Sytra AI

You are applying keep drop stata under deadline pressure, and one unnoticed data issue can invalidate the full analysis pass.

You will get a deterministic transform path from raw files to validated analysis input. This guide keeps the path anchored to turning raw partner files into one analysis-ready firm-year panel.

All examples tested in Stata 18 SE. Compatible with Stata 15+.

Quick Answer

  1. Start with a defined research task before running keep drop stata.
  2. Run keep only after preflight checks on keys, types, and missingness.
  3. Audit command output immediately and document expected vs observed counts.
  4. Add a reusable QA block focused on key uniqueness, row counts, and type stability.

Execution Blueprint: keep drop stata for turning raw partner files into one analysis-ready firm-year panel

Anchor the use case and run preflight checks

This workflow is built for turning raw partner files into one analysis-ready firm-year panel. A small key mismatch can break merges and remove observations without obvious warnings.

Run a deterministic setup first so every command in later sections executes against known data structure and known variable types.

If you are extending this pipeline, also review destring and real() in Stata: Convert String Numbers Safely and rename in Stata: Bulk Rename Patterns with Wildcards.

keep-drop-stata-subset-setup.do
stata
1clear all
2version 18
3set seed 260210
4set obs 1200
5gen firm_id = ceil(_n/12)
6gen year = 2014 + mod(_n,10)
7gen worker_id = _n
8gen education = 10 + floor(runiform()*8)
9gen wage = 18 + 0.8*education + 0.2*(year-2014) + rnormal(0,2)
10
11* Preflight checks
12assert !missing(firm_id, year)
13assert !missing(wage, education)
14count
. count
  1200
๐Ÿ’กUse realistic variable names
Keep names like wage, education, firm_id, and year so collaborators can audit logic quickly.

Execute keep with full diagnostics

Run keep as its own block and inspect output before proceeding. This preserves a clean debug boundary and supports peer review.

The command example below is complete and runnable; it is designed to mirror real panel workflows rather than toy x/y placeholders.

keep-drop-stata-subset-execution.do
stata
1clear all
2version 18
3set seed 260210
4set obs 1200
5gen firm_id = ceil(_n/12)
6gen year = 2014 + mod(_n,10)
7gen worker_id = _n
8gen education = 10 + floor(runiform()*8)
9gen wage = 18 + 0.8*education + 0.2*(year-2014) + rnormal(0,2)
10
11* Preflight checks
12assert !missing(firm_id, year)
13assert !missing(wage, education)
14count
15
16* ---- Section-specific continuation ----
17* Core execution block for keep drop stata
18count
19keep if year>=2018 & !missing(wage, education)
20keep firm_id worker_id year wage education
21count
22
23* Immediate output audit
24count
. count
  1200
โš ๏ธAudit before moving to the next stage
Immediately inspect outputs after each command block to prevent silent pipeline drift.

Harden for production: assertions, logs, and reusable checks

After command execution, enforce key uniqueness, row counts, and type stability so downstream inference and exports remain stable across reruns.

This final block makes the workflow team-ready: logs are captured, failures are explicit, and diagnostics are repeatable.

keep-drop-stata-subset-qa.do
stata
1clear all
2version 18
3set seed 260210
4set obs 1200
5gen firm_id = ceil(_n/12)
6gen year = 2014 + mod(_n,10)
7gen worker_id = _n
8gen education = 10 + floor(runiform()*8)
9gen wage = 18 + 0.8*education + 0.2*(year-2014) + rnormal(0,2)
10
11* Preflight checks
12assert !missing(firm_id, year)
13assert !missing(wage, education)
14count
15
16* ---- Section-specific continuation ----
17* Production hardening block
18capture log close
19log using keep-drop-stata-subset-qa.log, text replace
20
21count
22keep if year>=2018 & !missing(wage, education)
23keep firm_id worker_id year wage education
24count
25
26assert !missing(firm_id, year)
27count
28isid firm_id year
29log close
. isid firm_id year
. isid firm_id year
variables firm_id year uniquely identify the observations
๐Ÿ’กKeep a reusable QA footer
A standard QA footer with assert and count checks prevents repeat debugging in future projects.

Common Errors and Fixes

"variables firm_id year do not uniquely identify observations in the using data"

The side expected to be unique has duplicate keys.

Run duplicates report on key variables and aggregate or redefine key design.

. merge m:1 firm_id year using using_data.dta
variables firm_id year do not uniquely identify observations in the using data
r(459);
This causes the error
wrong-way.do
stata
merge m:1 firm_id year using using_data.dta
This is the fix
right-way.do
stata
use using_data.dta, clear
collapse (mean) education, by(firm_id year)
save using_data_unique.dta, replace
use master_data.dta, clear
merge m:1 firm_id year using using_data_unique.dta
error-fix.do
stata
1use using_data.dta, clear
2duplicates report firm_id year
3collapse (mean) education, by(firm_id year)
4isid firm_id year
. duplicates report firm_id year
Duplicates in terms of firm_id year

--------------------------------------
   Copies | Observations       Surplus
----------+---------------------------
        2 |          120            60
--------------------------------------

Command Reference

keep

Stata docs โ†’

Primary command reference for keep drop stata workflows in Stata.

keep varlist | keep if condition
Preflight checksValidate keys, types, and missingness before execution
Execution blockRun the command in an isolated, reviewable section
DiagnosticsInspect output immediately and compare against expectations
QA footerKeep assertions and logs for reproducible reruns

How Sytra Handles This

Sytra can execute keep drop stata as a staged workflow: preflight validation, runnable Stata code generation, and QA assertions before final output.

A direct natural-language prompt for this exact workflow:

sytra-prompt.txt
bash
Execute keep drop stata for a firm_id-year wage dataset. Use variables wage, education, firm_id, and year. Include preflight checks, runnable Stata code, output diagnostics, and post-command assertions with a log file.

Sytra catches these errors before you run.

Sytra can execute keep drop stata as a staged workflow: preflight validation, runnable Stata code generation, and QA assertions before final output.

Join the Waitlist โ†’

FAQ

What is the safest order for keep drop stata in a production do-file?

Use a three-step order: preflight checks, keep execution, and post-command assertions. This sequence catches breakpoints before models or exports depend on the result.

How do I verify that keep drop stata did not damage my sample?

Track count before and after each transformation, then validate key uniqueness and missingness changes on core variables. Keep those checks in the script, not in ad hoc console runs.

Which Stata versions are compatible with this workflow?

All examples are tested in Stata 18 SE and are compatible with Stata 15+, with installation checks included when community packages are used.

Related Guides

Written by Sytra Team
Research Engineering Team, Sytra AI

We build practical, reproducible workflows for Stata and R teams working on real empirical research pipelines.

#Stata#keep#Data Management

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