Forum Discussion
Calculating column values based on date match between tables
I'm attempting to perform a column calculation that will return a value based on the last date of an instrument calibration prior to a quality control check. I have two tables, Calibration and QC, which are related by instrument serial number. For each instrument, there may be multiple calibration dates and quality control checks, during which a result (Xq) is generated. The calculated column (cal check) should compare the difference between the QC check Xq and the Xq result of the last calibration prior to that check.
Example:
Calibration
| Serial | Cal Date | Cal Xq |
| 100141 | 12/5/19 14:12 | 0.081 |
| 100141 | 4/12/15 11:36 | 0.085 |
| 100290 | 6/16/15 9:19 | 0.077 |
| 100321 | 1/21/19 14:44 | 0.082 |
| 100321 | 1/21/19 11:12 | 0.079 |
| 100670 | 1/2/20 11:24 | 0.079 |
| 100670 | 9/4/18 15:39 | 0.081 |
QC
| Serial | QC Date | Cal Date | QC Xq | Cal Check |
| 100141 | 6/15/19 | 4/12/2015 | 0.081 | -4.71% |
| 100141 | 10/15/19 | 4/12/2015 | 0.082 | -3.53% |
| 100141 | 2/15/20 | 12/5/2019 | 0.079 | -2.47% |
| 100141 | 6/15/20 | 12/5/2019 | 0.08 | -1.23% |
| 100290 | 6/15/19 | 6/16/2015 | 0.079 | 2.60% |
| 100290 | 10/15/19 | 6/16/2015 | 0.078 | 1.30% |
| 100290 | 2/15/20 | 6/16/2015 | 0.077 | 0.00% |
| 100290 | 6/15/20 | 6/16/2015 | 0.077 | 0.00% |
| 100321 | 6/15/19 | 1/21/2019 | 0.08 | -2.44% |
| 100321 | 10/15/19 | 1/21/2019 | 0.081 | -1.22% |
| 100321 | 2/15/20 | 1/21/2019 | 0.079 | -3.66% |
| 100321 | 6/15/20 | 1/21/2019 | 0.082 | 0.00% |
| 100670 | 6/15/19 | 9/4/2018 | 0.079 | -2.47% |
| 100670 | 10/15/19 | 9/4/2018 | 0.077 | -4.94% |
| 100670 | 2/15/20 | 1/2/2020 | 0.082 | 3.80% |
| 100670 | 6/15/20 | 1/2/2020 | 0.081 | 2.53% |
Fortunately, there is a helper column in the QC table that lists when the last cal was performed. Unfortunately, it is just a date with no time stamp, whereas the Cal Date column in the Calibration table does include the time, and there may be multiple entries from the same day. If I were doing this in Excel, I would use an array to match serial number and cal date between the two tables to return the appropriate Cal Xq, and calculate the difference from there. If they are sorted newest-to-oldest in the table, it will give me the correct result. But, I'm new to Power BI and haven't found a comparable method of doing this with DAX.
Any help would be appreciated, thank you!
Hi Anonymous ,
here are two calc Columns that I think do the trick
last Cal Xq val = var serial = [Serial] var calDate = [QC Date] var maxDate = CALCULATE(MAX('Calibration'[Cal Date]), FILTER(Calibration, Calibration[Serial] = 'QC'[Serial] && Calibration[Cal Date] <= calDate )) return CALCULATE(MAX('Calibration'[Cal Xq]), FILTER('Calibration', Calibration[Serial] = serial && Calibration[Cal Date] = maxDate))var = DIVIDE([QC Xq], [last Cal Xq val])-1Hope this Helps
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11 Replies
Anonymous
Try this as a start. Add this calculated column to your QC table.
Cal Check Column = VAR _Serial = QC[Serial] VAR _Date = QC[QC Date] VAR _LastCal = CALCULATE( MAX (Calibration[Cal Date]), Calibration[Serial] = _Serial, Calibration[Cal Date] < _Date ) RETURN CALCULATE( MAX(Calibration[Cal Xq]), Calibration[Serial] = _Serial, Calibration[Cal Date] = _LastCal )-QC[QC Xq]That's definitely a promining start, thanks! I'm getting the error "A single value for column 'Serial' in table 'QC' cannot be determined." due to there being multiple entries in the table for each serial number. Using a MIN or MAX function yields incorrect results, as I think it's picking values associated with different dates in that case. Is there a way to specify that the variable only uses the serial number, date, and Xq from that row?
I appreciate the help!
Hi Anonymous ,
here are two calc Columns that I think do the trick
last Cal Xq val = var serial = [Serial] var calDate = [QC Date] var maxDate = CALCULATE(MAX('Calibration'[Cal Date]), FILTER(Calibration, Calibration[Serial] = 'QC'[Serial] && Calibration[Cal Date] <= calDate )) return CALCULATE(MAX('Calibration'[Cal Xq]), FILTER('Calibration', Calibration[Serial] = serial && Calibration[Cal Date] = maxDate))var = DIVIDE([QC Xq], [last Cal Xq val])-1Hope this Helps
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