added bland-altman on folders

docs/41_descriptive_statistics/utils.py

@@ -0,0 +1,25 @@
+# A function for drawing Bland-Altman plots
+# source: modified from https://stackoverflow.com/questions/16399279/bland-altman-plot-in-python
+import matplotlib.pyplot as plt
+import numpy as np
+
+def bland_altman_plot(data1, data2, measure="", title="", *args, **kwargs):
+    """
+    Draws a Bland-Altman plot from two lists of measurements. 
+    The physical measure should be given to put in axis labels.
+    The given title will show on top of the plot. 
+    """
+    data1     = np.asarray(data1)
+    data2     = np.asarray(data2)
+    mean      = np.mean([data1, data2], axis=0)
+    diff      = data1 - data2                   # Difference between data1 and data2
+    md        = np.mean(diff)                   # Mean of the difference
+    sd        = np.std(diff, axis=0)            # Standard deviation of the difference
+
+    plt.scatter(mean, diff, *args, **kwargs)
+    plt.axhline(md,           color='gray', linestyle='--')
+    plt.axhline(md + 1.96*sd, color='gray', linestyle='--')
+    plt.axhline(md - 1.96*sd, color='gray', linestyle='--')
+    plt.xlabel("average " + measure)
+    plt.ylabel("difference " + measure)
+    plt.title(title)

docs/_toc.yml

@@ -338,6 +338,7 @@ parts:
       - file: 41_descriptive_statistics/basic_descriptive_statistics
       - file: 41_descriptive_statistics/descriptive_statistics_label_images
       - file: 41_descriptive_statistics/Bland_altman_analysis
+      - file: 41_descriptive_statistics/bland_altman_on_folders_of_images
 
     # - file: 44_hypothesis_testing/readme
     #   sections: