# Quickstart

The goal of this document is to explain how the library works on a high-level.

## Datasets and Models¶

You can use doubtlab to check your own datasets for bad labels. Many of the methods that we provide are based on the interaction between a dataset and a model trained on that dataset. For example;

from sklearn.datasets import load_iris
from sklearn.linear_model import LogisticRegression

model = LogisticRegression(max_iter=1_000)
model.fit(X, y)


This examples shows a logistic regression model trained on the load_iris dataset. The model is able to make predictions on the dataset and it's also able to output a confidence score via model.predict_proba(X).

You could wonder. What might it mean if the confidence values are low? What might it mean if our model cannot make an accurate prediction on a datapoint that it's trained on? In both of these cases, it could be that nothing is wrong. But you could argue that these datapoints may be worth double-checking.

## Pipeline of Doubt Reasons¶

The doubtlab library allows you to define "reasons" to doubt the validity of a datapoint. The code below shows you how to build an ensemble of the two aforementioned reasons.

from doubtlab.ensemble import DoubtEnsemble
from doubtlab.reason import ProbaReason, WrongPredictionReason

# Define the reasons with a name.
reasons = {
"proba": ProbaReason(model=model, max_proba=0.55),
"wrong_pred": WrongPredictionReason(model=model),
}

# Put all the reasons into an ensemble
doubt = DoubtEnsemble(**reasons)


This ensemble represents a pipeline of reasons to doubt the validity of a label.

Internal Details

A DoubtEnsemble, technically, is just an ensemble of callables. You could also choose to use lambda functions to define a reason for doubt. The example below shows an example of a lambda function that's equivalent to what WrongPredictionReason would do.

DoubtEnsemble(
wrong_pred=lambda X, y: (model.predict(X) != y).astype(float16)
)


When it's time to infer doubt, the DoubtEnsemble will call each callable reason in order, passing X, y and listening for an array that contains "doubt-scores". These scores are just numbers, but they follow a few rules.

• When there is no doubt, the score should be zero
• The maximum doubt that a reason can emit is one
• The higher the doubt-score, the more likely doubt should be. For now the library emits 0/1 scores, but this may change in the future.

## Retreiving Examples to Check¶

There are multiple ways of retreiving the examples to check from the doubt pipeline.

### Get Indices¶

You could simply use the DoubtEnsemble.get_indices method to get the indices of the original data that are in doubt.

# Get the ordered indices of examples worth checking again
indices = doubt.get_indices(X, y)


In this case, you'd get an array with 7 elements.

array([ 77, 106, 126, 133,  83, 119,  70])


You can inspect the associated rows/labels of the examples via:

X[indices], y[indices]


### Get Predicates¶

While the indices are useful they don't tell you much about how the ordering took place. If you'd like to see more details, you can also retreive a dataframe with predicates that explain which rows triggered which reasons.

# Get the predicates, or reasoning, behind the order
predicates = doubt.get_predicates(X, y)


The predicates dataframe contains a column for each reason. The index refers to the row number in the original dataset. Let's check the top 10 rows.

predicates.head(10)

predicate_proba predicate_wrong_pred
77 1 1
106 1 1
126 1 0
133 1 0
83 0 1
119 1 0
70 0 1
105 0 0
107 0 0
104 0 0

There's a few things to observe here.

• The ensemble assumes that overlap between reasons matter is a reason to give a row priority, moving it up in the dataframe.
• The .get_indices method tells you what deserves checking and only returns candidates worth checking. The .get_predicates method tries to explain why these rows deserve to be checked and therefore returns a dataframe with a row for each row in X.
• The index of the predicates dataframe refers to rows in our original X, y arrays.

## Why do this exercise?¶

It's bad enough to have bad labels in your training data, but if you have bad labels in your validation then it's really game over for your machine learning models. There's ample evidence that many pre-trained academic models have suffered from this problem. So there's a legitimate concern that it may be a problem for your dataset as well.

The hope is that this library makes it just a bit easier for folks do to check their datasets for bad labels. It's an exercise worth doing and the author of this library would love to hear anekdotes.

## Does this scale?¶

You might be dealing with a large dataset, in which case you may want to be concious of compute time. Suppose you have a setup that looks something like:

from doubtlab.ensemble import DoubtEnsemble
from doubtlab.reason import ProbaReason, ShortConfidenceReason, LongConfidenceReason

# Suppose this dataset is very big and that this computation is heavy.
model = LogisticRegression(max_iter=1_000)
model.fit(X, y)

# This step might be expensive because internally we will be calling
# model.predict_proba(X) a lot!
ensemble = DoubtEnsemble(
proba=ProbaReason(model)
short=ShortConfidenceReason(model),
long=LongConfidenceReason(model)
)


Then you might wonder if we're able to speed things up by precomputing our .predict_proba()-values. You could use lambdas, but you can also use common utility methods that have been added to the reason classes. Most of our reasons implement a from_pred or from_proba method that you can use. See the API for more details.

That way, we can rewrite the code for a speedup.

import pandas as pd
from doubtlab.ensemble import DoubtEnsemble
from doubtlab.reason import ProbaReason, ShortConfidenceReason, LongConfidenceReason

# Suppose this dataset is very big and that this computation is heavy.
model = LogisticRegression(max_iter=1_000)
model.fit(X, y)

# Let's precalculate the proba values.
probas = model.predict_proba(X)

# We can re-use the probas below. Note that some reasons require extra information.
# Also beware that y and probas are globals now!
predicate_dict = dict(
proba=ProbaReason.from_proba(probas)
short=ShortConfidenceReason.from_proba(probas, y, classes=len(set(y)), threshold=0.2),
long=LongConfidenceReason.from_proba(probas, y, classes=len(set(y)), threshold=0.4)
)

# This dataframe now contains the predicates
pd.DataFrame(predicate_dict)


## Next Steps¶

You may get some more inspiration by checking some of the examples of this library.

Once you're ready to give the library a spin we encourage you to explore the suite of reasons that this library supports.

### General Reasons¶

• RandomReason: assign doubt randomly, just for sure
• OutlierReason: assign doubt when the model declares a row an outlier

### Classification Reasons¶

• ProbaReason: assign doubt when a models' confidence-values are low for any label
• WrongPredictionReason: assign doubt when a model cannot predict the listed label
• ShortConfidenceReason: assign doubt when the correct label gains too little confidence
• LongConfidenceReason: assign doubt when a wrong label gains too much confidence
• MarginConfidenceReason: assign doubt when there's a small difference between the top two class confidences
• DisagreeReason: assign doubt when two models disagree on a prediction
• CleanlabReason: assign doubt according to cleanlab

### Regression Reasons¶

• AbsoluteDifferenceReason: assign doubt when the absolute difference is too high
• RelativeDifferenceReason: assign doubt when the relative difference is too high
• StandardizedErrorReason: assign doubt when the absolute standardized residual is too high

If you think there's a reason missing, feel free to mention it on GitHub.