# logloss.integer.md

|                 |                 |
| --------------- | --------------: |
| logloss.integer | R Documentation |

### Logarithmic Loss

#### Description

A generic S3 function to compute the *logarithmic loss* score for a\
classification model. This function dispatches to S3 methods in`logloss()` and performs no input validation. If you supply NA values or\
vectors of unequal length (e.g. `length(x) != length(y)`), the\
underlying `C++` code may trigger undefined behavior and crash your `R`\
session.

**Defensive measures**

Because `logloss()` operates on raw pointers, pointer-level faults (e.g.\
from NA or mismatched length) occur before any `R`-level error handling.\
Wrapping calls in `try()` or `tryCatch()` will *not* prevent `R`-session\
crashes.

To guard against this, wrap `logloss()` in a "safe" validator that\
checks for NA values and matching length, for example:

{% code overflow="wrap" lineNumbers="true" %}

```r
safe_logloss <- function(x, y, ...) {
  stopifnot(
    !anyNA(x), !anyNA(y),
    length(x) == length(y)
  )
  logloss(x, y, ...)
}
```

{% endcode %}

Apply the same pattern to any custom metric functions to ensure input\
sanity before calling the underlying `C++` code.

#### Usage

```r
## S3 method for class 'integer'
logloss(actual, response, normalize = TRUE, ...)
```

#### Arguments

|             |                                                                                                                                                                                                                                                                                        |
| ----------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `actual`    | A vector length `n`, and `k` levels. Can be of integer or factor.                                                                                                                                                                                                                      |
| `response`  | A `n \times k` \<double>-matrix of predicted probabilities. The `i`-th row should sum to 1 (i.e., a valid probability distribution over the `k` classes). The first column corresponds to the first factor level in `actual`, the second column to the second factor level, and so on. |
| `normalize` | A \<logical>-value (default: TRUE). If TRUE, the mean cross-entropy across all observations is returned; otherwise, the sum of cross-entropies is returned.                                                                                                                            |
| `...`       | Arguments passed into other methods.                                                                                                                                                                                                                                                   |

#### Value

A \<double>

#### References

MacKay, David JC. Information theory, inference and learning algorithms.\
Cambridge university press, 2003.

Kramer, Oliver, and Oliver Kramer. "Scikit-learn." Machine learning for\
evolution strategies (2016): 45-53.

Virtanen, Pauli, et al. "SciPy 1.0: fundamental algorithms for\
scientific computing in Python." Nature methods 17.3 (2020): 261-272.

#### Examples

```r
## Classes and
## seed
set.seed(1903)
classes <- c("Kebab", "Falafel")

## Generate actual
## and predicted response
## probabilities
actual_classes <- factor(
x = sample(x = classes, size = 1e3, replace = TRUE),
levels = c("Kebab", "Falafel")
)

response <- runif(n = 1e3)

## Evaluate performance
SLmetrics::logloss(
   actual    = actual_classes, 
   response  = cbind(
 response,
 1 - response
   )
)

## Generate observed
## frequencies 
actual_frequency <- sample(10L:100L, size = 1e3, replace = TRUE)

SLmetrics::logloss(
   actual    = actual_frequency, 
   response  = response
)


```

```

</div>

```


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