Documentation

Command reference, language syntax, and practical recipes for econometric work.

Language basics

Hayashi uses a Stata-like command grammar with modern expression support. Statements are separated by newlines or semicolons. Results are printed unless suppressed with a trailing semicolon.

basics.hay

// Load data
load "wage1.csv" as df

// Variables and assignment
let x = 10
let y = x + 5

// Conditional
if y > 10 {
  print("large")
}

// Loop
for i in 1..5 {
  print(i)
}

Data I/O

Hayashi reads and writes several tabular formats. ODBC is available as an optional feature.

Command	Description
`load "file.csv" as df`	Load CSV/TSV
`load "file.json" as df`	Load JSON array
`load "file.dta" as df`	Load Stata .dta
`load "file.xlsx" as df`	Load Excel sheet
`load "file.parquet" as df`	Load Parquet
`load "sqlite://path.db" as df`	SQL query to DataFrame
`save df, "csv", "out.csv"`	Save DataFrame

Block expressions & output control

A block can be used as an expression: it runs statements and returns the last expression. Variables declared inside are local to the block.

blocks.hay

let df = {
  let raw = load("data.csv")
  generate raw y = log(x)
  keep(raw, ["date", "y"])
  raw
}

quietly on
let m = merge(df2, df3, key=id, type=inner)
quietly off

print("done")

quietly on suppresses automatic output from statements and estimators. print(...) and display ... still appear. The flag is scope-aware: toggling inside a block reverts when the block ends.

Data & I/O utilities

Common helpers for missing values, file-system checks, and simple caching.

Command	Description
`dropna(df, col1, col2)`	Remove rows with NaN
`ffill(df)`	Forward-fill NaN in float columns
`file_exists("path")`	Check if path exists
`ensure_dir("cache")`	Create directory if missing
`write("text", "file.txt")`	Write string to file
`export(df, "csv", "out.csv")`	Save DataFrame

Estimators

All estimators share a common formula syntax and return a model object with post-estimation methods.

Command	Family
`ols(y ~ x1 + x2, df)`	Ordinary least squares
`iv(y ~ x1 + x2, ~ z1 + z2, df)`	Instrumental variables / 2SLS
`logit(y ~ x1 + x2, df)`	Binary logistic regression
`probit(y ~ x1 + x2, df)`	Binary probit regression
`poisson(y ~ x1 + x2, df)`	Poisson regression
`nbreg(y ~ x1 + x2, df)`	Negative binomial
`tobit(y ~ x1 + x2, df)`	Censored regression
`qreg(y ~ x1 + x2, df, tau=0.5)`	Quantile regression
`fe(y ~ x1 + x2 \| id, df)`	Panel fixed effects
`re(y ~ x1 + x2 \| id, df)`	Panel random effects
`ab(y ~ x1 + x2 \| id + year, df)`	Arellano-Bond dynamic panel
`heckman(y ~ x1 + x2, s ~ z1 + z2, df)`	Heckman two-step
`garch(y ~ 1, df, p=1, q=1)`	GARCH volatility
`var(df, lags=2)`	Vector autoregression
`vecm(df, lags=2, rank=1)`	Vector error correction
`did(y ~ treat + post, df)`	Difference-in-differences
`gmm(y ~ x1, df, instruments=z1)`	Generalized method of moments
`rolling(y ~ x1 + x2, df, window=30)`	Rolling OLS with optional `date=date_col`

Post-estimation

After fitting a model, use these verbs for inference, prediction, and diagnostics.

Command	Description
`test(model, "x1 = 0")`	Wald test
`predict(model, df)`	Generate predictions
`margins(model, dydx(x1))`	Marginal effects
`bootstrap(model, reps=1000)`	Bootstrap inference
`estat(model, "vif")`	Diagnostic statistics
`nlcom(model, "x1/x2")`	Nonlinear combination
`esttab(model)`	Regression table output
`tidy(model)`	Convert model to a tidy DataFrame of coefficients
`glance(model)`	Convert model to a one-row summary DataFrame

Modern syntax

Hayashi adds modern conveniences to the Stata-like grammar without breaking the REPL workflow.

modern.hay

// Pipes
let df2 = df |> filter(educ > 12) |> mutate(lwage = log(wage))

// F-strings
print("R² = {model.r2}")

// Match expression
let sign = match coef > 0 { true => "+", false => "-" }

// Functions
fn my_mean(x) {
  return sum(x) / len(x)
}

Recipe: rolling CAPM

A complete daily CAPM pipeline with rolling betas.

capm.hay

import("sheep-farm/hayahoo", as=yahoo)

let asset = yahoo::history("AAPL", {"range": "50y", "interval": "1d"})
generate asset asset_ret = log(close / L.close)
asset |> keep(["date", "asset_ret"])

let market = yahoo::history("SPY", {"range": "50y", "interval": "1d"})
generate market market_ret = log(close / L.close)
market |> keep(["date", "market_ret"])

let merged = merge(asset, market, key=date, type=inner)

let with_rf = merged
generate with_rf excess_asset = asset_ret
generate with_rf excess_market = market_ret
let df = dropna(with_rf, excess_asset, excess_market)

let model = df |> ols(excess_asset ~ excess_market, _)
print(model)

let roll = rolling(excess_asset ~ excess_market, df, window=252, date=date)
let betas = tidy(roll)
let coefs = betas["excess_market"]

print("mean =", mean(coefs))
print("sd   =", sd(coefs))
print("min  =", min(coefs))
print("max  =", max(coefs))

CLI commands

Command	Description
`hay script.hay`	Run a script
`hay`	Start REPL
`hay install user/repo`	Install plugin
`hay update [user/repo]`	Update plugin(s)
`hay remove user/repo`	Remove plugin
`hay list`	List installed plugins
`hay validate`	Run empirical validation suite
`hay dist-update`	Update Hayashi binary to latest release