initial impl for giving default pyam dataframes

pyam/utils.py

@@ -367,3 +367,29 @@ def to_int(x, index=False):
         return x
     else:
         return _x
+
+
+def df_to_pyam(df, **kwargs):
+    numeric_cols = ['year']
+    defaults = {
+        x: x if x not in numeric_cols else 0 for x in pyam.utils.GROUP_IDX
+    }
+    defaults.update(kwargs)
+
+    def _apply_defaults(df, defaults):
+        for col, val in defaults.items():
+            df[col] = val
+        return df
+
+    # maybe only needed if variable is missing?
+    cols = list(set(df.columns) - set(pyam.utils.LONG_IDX))
+    idx = list(set(df.columns) & set(pyam.utils.LONG_IDX))
+    df = df.set_index(idx)
+    dfs = []
+    for col in cols:
+        _df = df[col].to_frame().rename(columns={col: 'value'})
+        _df['variable'] = col
+        dfs.append(_df.reset_index())
+    df = pd.concat(dfs)
+    df = _apply_defaults(df, defaults)
+    return pyam.IamDataFrame(df)