Now works with example file

app.py

@@ -34,6 +34,26 @@ def add_nodes(G, df):
     G.add_nodes_from(nodes)
     return G
 
+def find_columns(column, columns):
+
+    if column in columns:
+        selected = column
+    else:
+        columns.append('')
+        selected = ''
+
+    # Let user select target.
+    selected = st.selectbox(
+        label = f"Which one is the {column} column?",
+        options=columns,
+        format_func=lambda x: 'Select an option' if x == '' else x,
+        index=columns.index(selected),
+        key=column
+    )
+
+    return selected
+
+
 # Set oage config and CSS.
 st.set_page_config(page_title='CSV→GEXF', page_icon='🎭')
 st.markdown(info.css, unsafe_allow_html=True)
@@ -46,12 +66,14 @@ st.markdown(
     with Gephi and [Gephi Light](https://gephi.org/gephi-lite/).*"""
 )
 
-# Print explainer.
+try:
-expl = st.expander(label="More info")
+    # Print explainer.
-with expl:
+    expl = st.expander(label="More info")
+    with expl:
         st.write(info.explainer)
 
-with st.form("files"):
+
+
     # Ask for nodes file.
     csv_nodes = st.file_uploader(
         label="Upload file with **nodes** (if you have one).", key="nodes", help=f'[Example]({info.node_example})'
@@ -60,60 +82,72 @@ with st.form("files"):
     # Ask for relations file.
     csv_edges = st.file_uploader(label="Upload file with **relations**.", key="relations", help=f'[Example]({info.relations_example})')
 
-    sep = st.radio('Separator in your files:', options=['comma ( , )', 'semicolon ( ; )', 'tab ( \u21E5 )'], help='What are the values in your files separated with?')
+    col1, col2 = st.columns([1,2])
+
+    # Chose separator
+    with col1:
+        # Set standard separator.
+        st.session_state["sep"] = ','
 
-    files_uploaded = st.form_submit_button("Done")
+        # Ask for separator.
+        sep = st.radio(
+            'Separator in your files:', 
+            options=['comma ( , )', 'semicolon ( ; )', 'tab ( \u21E5 )', 'pipe (|)', 'space ( )'], 
+            help='What are the values in your files separated with?'
+            )
         
-if files_uploaded:
+        separators = {'comma ( , )': ',', 'semicolon ( ; )': ';', 'tab ( \u21E5 )': '\t', 'pipe (|)': '|', 'space ( )': ' '}
-    separators = {'comma ( , )': ',', 'semicolon ( ; )': ';', 'tab ( \u21E5 )': '\t'}
-    if 'sep' not in st.session_state:
         st.session_state["sep"] = separators[sep]
 
+    # Preview file
+    with col2: 
+        preview = st.button('Preview file.')
+        if preview:
+            st.dataframe(pd.read_csv(csv_edges, sep=st.session_state["sep"]))
+
+
+    files_uploaded = st.button('Done', 'files_uploaded')
+    print(st.session_state['files_uploaded'])
+
+    if files_uploaded or 'files_already_uploaded' in st.session_state:
+        st.session_state['files_already_uploaded'] = True
+
         if csv_edges == None:
             st.markdown(':red[You need to upload a file with relations.]')
             st.stop()
 
+        print('SEP', st.session_state["sep"])
+        try:
             df = pd.read_csv(csv_edges, sep=st.session_state["sep"])
+        except pd.errors.EmptyDataError:
+            st.markdown(':red[Have you chosen the right kind of separator?]')
+            st.stop()
             
         df.rename({'type': 'relation_type'}, inplace=True, axis=1) # 'type' can't be used as attribute.
         df.columns = [i.lower() for i in df.columns] # Remove capital letters from column names.
-    columns = df.columns.tolist()
 
-    # Find and store target column.
+        with st.form('select_columns'):
-    if "target" not in st.session_state:
-        if "target" in columns:
-            preselected_target = "target"
-        else:
-            columns.append("")
-            preselected_target = len(columns) - 1
             
-        st.session_state["target"] = st.selectbox(
+            # Find and store target column.
-            label="Which one is the target column?",
+            target = find_columns('target', df.columns.tolist())
-            options=columns,
-            index=columns.index(preselected_target),
-        )
 
             # Find and store source column.
-    if "source" not in st.session_state:
+            source = find_columns('source', df.columns.tolist())
-        if "source" in columns:
-            preselected_source = "source"
-        else:
-            columns.append("")
-            preselected_source = len(columns) - 1
 
-        st.session_state["source"] = st.selectbox(
+            # Confirm choise.
-            label="Which one is the source column?",
+            columns_selected = st.form_submit_button("Done")
-            options=columns,
-            index=columns.index(preselected_source),
-        )
         
+        if columns_selected:
             # Remove source and target columns from list of options.
+            columns = df.columns.tolist()
             columns.remove(st.session_state["target"])
             columns.remove(st.session_state["source"])
             
             if all([st.session_state["source"] != "", st.session_state["target"] != ""]):
                 source = st.session_state["source"]
                 target = st.session_state["target"]
+
+                # Let the user chose what columns that should be included.
                 chosen_columns = st.multiselect(
                     label="Chose other columns to include.", options=columns, default=columns
                 )
@@ -121,17 +155,8 @@ if files_uploaded:
                 if csv_nodes != None: # When a nodes file is uploaded.
                     df_nodes = pd.read_csv(csv_nodes, sep=st.session_state["sep"])
                     df_nodes.columns = [i.lower() for i in df_nodes.columns] # Remove capital letters from column names.
-            columns = df_nodes.columns.tolist()
+
-            if "label" in columns:
+                    label_column = find_columns('label', df_nodes.columns.tolist())
-                preselected_label = "label"
-            else:
-                columns.append("")
-                preselected_label = len(columns) - 1
-            label_column = st.selectbox(
-                label="Which one is the label column in the nodes file?",
-                options=columns,
-                index=columns.index(preselected_label),
-            )
                     df_nodes.set_index(label_column, inplace=True)
 
                 else: # If no node file provided.
@@ -141,7 +166,6 @@ if files_uploaded:
                     )
                     df_nodes.set_index("labels", inplace=True)
 
-
                 # Make empty graph.
                 G = nx.MultiDiGraph()
                 # Add nodes.
@@ -159,3 +183,7 @@ if files_uploaded:
                 st.download_button(
                     "Download gexf-file", graph_text, file_name=gexf_file
                 )
+                st.write('Import the file to Gephi/Gephi Light, or try [Gephisto](https://jacomyma.github.io/gephisto/) to get an idea of the network.')
+
+except:
+    st.markdown(':red[Something went wrong, please try again or [write to me](https://twitter.com/lasseedfast).]')