How to transfer pandas .plot() to Matplotlib .errorbar()

Question

I'm looking to plot error bars on a line plot I did using pandas's .plot() function

scores_xgb.plot(x='size', y='MSE_mean_tot', kind='line',logx=True,title='XGBoost 5 samples, 5 fold CV')

Running this gives me the following plot:

For plotting the error bars, I choose to use .errorbar() from Matplotlib. When running the cell

plt.errorbar(x=scores_xgb.size, y=scores_xgb.MSE_mean_tot, yerr=std_xgb ,title='XGBoost 5 samples, 5 fold CV')
plt.show()

I receive the following error message:

ValueError: 'x' and 'y' must have the same size

This confuses me, as I use the same Dataframe in both examples, each time using the same variable for x and y respectively, therefore it has the same size (12) both times.

NB: the yerr = std_xgb also has size 12.

Yes, I have a column size in this dataframe. It contains information about the number of rows of other dataframes on which my models are trained. — CrazyTiger
– CrazyTiger, Commented Mar 22, 2022 at 14:39

user17242583 · Accepted Answer · 2022-03-21 18:23:48Z

1

There is a property on pandas.DataFrame objects named size, and it's a number, equal to the number of cells in the DataFrame (the product of the values in df.shape). You're trying to access a column named size, but pandas chooses the property named size before it chooses the column name size. Since the single number has a shape of 1 but the columns in the dataframe have a length of 12, you're getting a shape mismatch.

Instead, use strings to index the dataframe and get the the columns:

plt.errorbar(x=scores_xgb['size'], y=scores_xgb['MSE_mean_tot'], yerr=std_xgb, title='XGBoost 5 samples, 5 fold CV')

answered Mar 21, 2022 at 18:23

user17242583

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