Creating a Table

To use the QUERY_TABLE function, you have to create a table first with the BUILD_TABLE command. Tables are created from vectors (one-dimensional variables) that contain the same number of elements. Each variable becomes, in effect, a column in the table. Before you attempt to create a table, however, you need to read your data into a set of variables.

For detailed information on reading data into PV‑WAVE, see Chapter 9: Working with Data Files in the PV‑WAVE Programmer’s Guide.

Once your data is read into a set of equal-sized variables, use the BUILD_TABLE function to build a table. Each variable becomes, in effect, a separate column in the table. Once the variables are placed into a table, QUERY_TABLE can be used to subset and manipulate the data.

note

In PV‑WAVE, a table is represented as an array of structures. You do not have to understand or use structures to use the table functions. However, you may want to review the chapter on structures, Working with Structures, in the PV‑WAVE Programmer’s Guide, before you proceed to learn about the table functions. Also see the section "Tables and Structures".

The table columns and the original input variables are separate. The original variables are not removed when the table is created.

The following example assumes that you have defined eight variables and read data into them. The data for this example represents information collected from a company-wide telephone system. The variable names are: DATE, TIME, DUR, INIT, EXT, COST, AREA, and NUMBER.

The following command builds an eight-column table from the telephone data variables. Note that BUILD_TABLE takes one parameter, a string containing the names of the variables.

DATE	TIME	DUR	INIT	EXT	COST	AREA	NUMBER
901002	093200	21.40	TAC	311	5.78	215	2155554242
901002	094700	1.05	BWD	358	0.0	303	5553869
901002	094700	17.44	EBH	320	4.71	214	2145559893
901002	094800	16.23	TDW	289	0.0	303	5555836
901002	094800	1.31	RLD	248	.35	617	6175551999
901003	091500	2.53	DLH	332	.68	614	6145555553
901003	091600	2.33	JAT	000	0.0	303	555344
901003	091600	.35	CCW	418	.27	303	5555190
901003	091600	1.53	SRB	379	.41	212	2125556618
901004	094700	.80	JAT	000	0.0	303	555320
901004	094900	1.93	SRB	379	.52	818	8185552880
901004	095000	3.77	DJC	331	1.02	512	5125551228
901004	095100	.16	GWP	370	0.0	303	5551245

note	You can format and print a table so that it appears approximately like the above example. For information on printing table data, see "Formatting and Printing Tables".

You can use the INFO command to view the table structure. Tables are represented as arrays of structures (for more information on this, see "Tables and Structures"). Thus, the Structure keyword is used with the INFO command to obtain information on tables, for example:

DATE	LONG	901002
TIME	LONG	93200
DUR	FLOAT	21.4000
INIT	STRING	'TAC'
EXT	LONG	311
COST	FLOAT	5.78000
AREA	LONG	215
NUMBER	STRING	'2155554242'

A table is built from vector (one-dimensional array) variables only. You cannot include expressions in the BUILD_TABLE function. For example, the following BUILD_TABLE call is not allowed:

However, you can achieve the desired results by performing the array subsetting operations first, then using the resulting variables in BUILD_TABLE. For example:

From any given set of equal-length variables, BUILD_TABLE can use all or some of the variables to build a table, and the table’s columns can be placed in any order.

The following table contains just four columns instead of eight. Also, the columns appear in a different order than in the previous example.

DATE	EXT	DUR	COST
901002	311	21.40	5.78
901002	358	1.05	0.0
901002	320	17.44	4.71
901002	289	16.23	0.0
901002	248	1.31	.35
901003	332	2.53	.68
901003	000	2.33	0.0

By default, BUILD_TABLE uses the original variable names as the names of the table columns. You can rename columns by including the new name or “alias” directly in the BUILD_TABLE command. Place the alias immediately after the original variable name. For example, the previous new_tbl table can be created with different column names:

The resulting table is identical to the table created in the previous section, except for the column names. To see the structure of this new table, enter:

CALL_DATE	LONG	901002
EXTENSION	LONG	311
CALL_LENGTH	FLOAT	21.4000
CALL_COST	FLOAT	5.78000