Update app.py

app.py

@@ -46,4 +46,17 @@ pg = st.navigation(pages=[start_page, type_text_page, upload_file_page, about_pa
 #pg = st.navigation({"Chapter_Index": [start_page], "Demo": [type_text_page, upload_file_page], "About": [about_page]}) # WITH SECTIONS
 pg.run() 
 
-st.sidebar.text("Project by JA-RAD")
+st.sidebar.text("Project by JA-RAD")
+
+def filter_chapters_env(df, chapter_column_name):
+    chapter_names = st.sidebar.multiselect(
+        label="Chapter Name", options=df[chapter_column_name].unique(), default=st.session_state.get("chapter_names"), key='filter_chapters', on_change=update_chapters
+    )
+    st.session_state["chapter_names"] = chapter_names
+
+    if chapter_names:
+        df = df[df["chapter_name"].isin(chapter_names)]
+    return df
+
+def update_chapters():
+   st.session_state["chapter_names"] = st.session_state.filter_chapters