StandardScaler()
# the mean value in each column is assigned a value of 0.0 if present
# and the values are centered around 0.0 with values both positive and negative.
MinMaxScaler()
# the largest raw value for each column now has the value 1.0
# and the smallest value for each column now has the value 0.0.
# for more information and examples :
# https://machinelearningmastery.com/standardscaler-and-minmaxscaler-transforms-in-python/