title: GridSearchCV on a pipeline with standardscaler, PCA & lasso
body: <p>Assume that I am doing GridSearchCV on a pipeline with [StandardScaler, PCA &amp; Lasso], where the grid search is over 2 values for a PCA parameter and 3 values for a Lasso parameter (thus 6 possible parameter combinations). When doing CV, for a given fold does the algorithm standardize only the train set in that fold (<em>i.e.,</em> not include the fold's test set for determining mean/variance of the standardizer) or does it standardize the entire data set outside of the folds (in which case there is only one Standardizing done for the entire grid search procedure)?</p>