27.13.10 PgxFrame Helpers

PgxFrame supports the following operations:

  • head
  • tail
  • select
  • renameColumns

Head Operation

The head operation can be used to only keep the first rows of a PgxFrame. (The result is deterministic only for ordered PgxFrame.) 

opg4j> vecFrame.head(2).print()
vecFrame.head(2).print();
vec_frame.head(2).print()

The output appears as follows:

+-----------------------------------------------------------+
| intProp | intProp2 | vectProp    | stringProp | vectProp2 |
+-----------------------------------------------------------+
| 0       | 2        | 0.1;0.2;0.3 | testProp0  | 0.1;0.2   |
| 1       | 1        | 0.1;0.2;0.3 | testProp10 | 0.1;0.2   |
+-----------------------------------------------------------+

Tail Operation

The tail operation can be used to only keep the last rows of a PgxFrame. (The result is deterministic only for ordered PgxFrame). 

opg4j> vecFrame.tail(2).print()
vecFrame.tail(2).print();
vec_frame.tail(2).print()

The output appears as follows:

+-----------------------------------------------------------+
| intProp | intProp2 | vectProp    | stringProp | vectProp2 |
+-----------------------------------------------------------+
| 2       | 3        | 0.1;0.2;0.3 | testProp30 | 0.1;0.2   |
| 3       | 1        | 0.1;0.2;0.3 | testProp40 | 0.1;0.2   |
+-----------------------------------------------------------+

Select Operation

The select operation can be used to keep only a specified list of columns of an input PgxFrame. 

opg4j> var vecFrameSelected = vecFrame.select("vectProp2", "vectProp", "stringProp")
PgxFrame vecFrameSelected = vecFrame.select("vectProp2","vectProp","stringProp");
vec_frame_selected = vec_frame.select("vectProp2","vectProp","stringProp")

The result may appear as follows:

+--------------------------------------+
| vectProp2 | vectProp    | stringProp |
+--------------------------------------+
| 0.1;0.2   | 0.1;0.2;0.3 | testProp0  |
| 0.1;0.2   | 0.1;0.2;0.3 | testProp10 |
| 0.1;0.2   | 0.1;0.2;0.3 | testProp20 |
| 0.1;0.2   | 0.1;0.2;0.3 | testProp30 |
| 0.1;0.2   | 0.1;0.2;0.3 | testProp40 |
+--------------------------------------+

Rename PgxFrame Columns

You can rename the columns in a PgxFrame to customized names as follows: 

opg4j> var vecFrameRenamed = vecFrame.renameColumns(
  renaming("vectProp2", "vectProp2_renamed"),
  renaming("vectProp", "vectProp_renamed"),
  renaming("stringProp", "stringProp_renamed")
)
PgxFrame vecFrameRenamed = vecFrame.renameColumns(renaming("vectProp2", "vectProp2_renamed"),
                                            renaming("vectProp", "vectProp_renamed"),
                                            renaming("stringProp", "stringProp_renamed"));
vec_frame_renamed = vec_frame.rename_columns({"vectProp2": "vectProp2_renamed", "vectProp": "vectProp_renamed", "stringProp": "stringProp_renamed"})

The renamed PgxFrame appears as follows: 

+--------------------------------------------------------------------------------+
| intProp | intProp2 | vectProp_renamed | stringProp_renamed | vectProp2_renamed |
+--------------------------------------------------------------------------------+
| 0       | 2        | 0.1;0.2;0.3      | testProp0          | 0.1;0.2           |
| 1       | 1        | 0.1;0.2;0.3      | testProp10         | 0.1;0.2           |
| 1       | 2        | 0.1;0.2;0.3      | testProp20         | 0.1;0.2           |
| 2       | 3        | 0.1;0.2;0.3      | testProp30         | 0.1;0.2           |
| 3       | 1        | 0.1;0.2;0.3      | testProp40         | 0.1;0.2           |
+--------------------------------------------------------------------------------+

Parent topic: PgxFrames Tabular Data-Structure