R practice in Statistics
Browse the rooms before signing in. All rooms are free with an account. Practice does not issue certificates.
Clean the Readings
A missing reading is not zero; missingness mechanisms may still affect the resulting estimate.
na. Free with an account.
Count the Passes
A score exactly sixty passes; negative or lower scores do not.
numeric. Free with an account.
Keep the Gains
Break-even days are not gains and must be excluded.
indexing. Free with an account.
Tally the Ballots
Count before choosing a winner, and make tie handling explicit.
characters. Free with an account.
Fold the Receipts
Multiplication combines factors; a zero makes the total product zero.
functionals. Free with an account.
Rank the Leaderboard
Return ranks in original observation order, not a sorted copy of the values.
mutate-arrange. Free with an account.
Square the Batch
Mapping a function does not inherently remove iteration or guarantee faster execution.
apply. Free with an account.
Summarize the Cohort
The result order is a then b regardless of which group has the larger mean.
grouping. Free with an account.
Estimate the Odds
The quarter-circle area supplies the target; the realized simulation is not exactly pi. Preserve draw order for reproducibility.
simulation. Free with an account.
Flag the Anomaly
A fence flags unusual values without proving measurement error; equality to a fence is not outside.
outliers. Free with an account.
Read the Z-Table
The CDF is accumulated area, not density height at z.
continuous. Free with an account.
Size Up the Spread
The coefficient of variation is unitless but depends on a meaningful measurement origin.
spread. Free with an account.
Bracket the Mean
The interval concerns a population mean under independent-observation assumptions, not a range covering individual readings.
ci. Free with an account.
Fit the Line
The fixed predictor spacing makes the slope half the difference between the final and first response.
leastsquares. Free with an account.
Score the Fit
In-sample explained variation is not a future performance guarantee.
fit. Free with an account.
Test the Claim
The independent-group test does not assume equal variances and does not establish causation.
ttest. Free with an account.
Bootstrap the Error
The output estimates sampling variability under the empirical distribution, not the spread of raw observations.
sampling. Free with an account.
Cross-Validate
Training rows must exclude the held-out fold. These folds are for independent observations, not time-series forecasting.
crossval. Free with an account.
Forecast Next Quarter
Recover intercept=mean(current)-phi*mean(past), then add it to phi*last. Omitting it would use a different model from the one fitted.
forecast. Free with an account.
Label the Model Fit
These classroom labels describe in-sample fit, not causal validity or held-out accuracy. Compare unrounded input.
report. Free with an account.