## ref()
Reference a column from the reference data for aggregate comparisons.
Usage
``` python
ref(column_name)
```
This function is used with aggregate validation methods (like [col_sum_eq](Validate.col_sum_eq.md#pointblank.Validate.col_sum_eq), [col_avg_gt](Validate.col_avg_gt.md#pointblank.Validate.col_avg_gt), etc.) to compare the aggregate value of a column in the main data against the aggregate value of a column in the reference data.
To use this function, you must first set the reference data on the [Validate](Validate.md#pointblank.Validate) object using the `reference=` parameter in the constructor.
## Parameters
`column_name: str`
The name of the column in the reference data to compute the aggregate from.
## Returns
`ReferenceColumn`
A reference column marker that indicates the value should be computed from the reference data.
## Examples
Suppose we have two DataFrames: a current data table and a reference (historical) table. We want to validate that the sum of a column in the current data matches the sum of the same column in the reference data.
``` python
import pointblank as pb
import polars as pl
# Current data
current_data = pl.DataFrame({"sales": [100, 200, 300]})
# Reference (historical) data
reference_data = pl.DataFrame({"sales": [100, 200, 300]})
validation = (
pb.Validate(data=current_data, reference=reference_data)
.col_sum_eq("sales", pb.ref("sales"))
.interrogate()
)
validation
```
|
|
STEP |
COLUMNS |
VALUES |
TBL |
EVAL |
UNITS |
PASS |
FAIL |
W |
E |
C |
EXT |
| #4CA64C |
1 |
col_sum_eq()
|
sales |
ref('sales') |
 |
✓ |
1 |
1
1.00 |
0
0.00 |
-- |
-- |
-- |
-- |
You can also compare different columns or use tolerance:
``` python
current_data = pl.DataFrame({"revenue": [105, 205, 305]})
reference_data = pl.DataFrame({"sales": [100, 200, 300]})
# Check if revenue sum is within 10% of sales sum
validation = (
pb.Validate(data=current_data, reference=reference_data)
.col_sum_eq("revenue", pb.ref("sales"), tol=0.1)
.interrogate()
)
validation
```
|
|
STEP |
COLUMNS |
VALUES |
TBL |
EVAL |
UNITS |
PASS |
FAIL |
W |
E |
C |
EXT |
| #4CA64C |
1 |
col_sum_eq()
|
revenue |
ref('sales')
tol=0.1 |
|
✓ |
1 |
1
1.00 |
0
0.00 |
-- |
-- |
-- |
-- |
#### See Also
[The](The.md)