scaler.fit_transform

`scaler.fit_transform` is a method used for preprocessing data in machine learning. It is a combination of two methods - `fit` and `transform`.

`fit` is used to compute the scaling parameters (mean and standard deviation) of the data based on the training set. These scaling parameters are used to transform the data so that it has a mean of 0 and a standard deviation of 1.

`transform` is used to apply the scaling parameters (mean and standard deviation) to the data to transform it into the scaled version.

In summary, `scaler.fit_transform` fits the scaler to the training data and scales both the training and testing data using the same scaling parameters. This ensures that the testing data is transformed in the same way as the training data, which is necessary for accurate model performance.