Creating bar plot with frequency distribution based
What you are looking for is a histogram. It plots the distribution of a given series of values. So, you can just extract the values that you want to plot from your dataframe and then use matplotlib's histogram function. Here is the code:

import matplotlib.pyplot as plt
to_plot = data.loc[df['Size']==1]['Value']
plt.hist(to_plot)
plt.show()


This is the output I get, note that I haven't done any formatting, this is just the raw output.


The above option is more flexible. But in your case you can also use the following:

import matplotlib.pyplot as plt
to_plot = data.loc[df['Size']==1]['Value']
to_plot.value_counts().plot.bar()