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https://github.com/nushell/nushell
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25a8caa9b0
* WIP: experiment with simpler expressions * fix simple invoke * update tests * fix a few tests * Make paren parsing more robust * fix external args * Remove old invocation * Update tests * Update tests
76 lines
No EOL
3.4 KiB
Markdown
76 lines
No EOL
3.4 KiB
Markdown
# empty?
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Check for empty values. Pass the column names to check emptiness. Optionally pass a block as the last parameter if setting contents to empty columns is wanted.
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## Examples
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Check if a value is empty
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```shell
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> echo '' | empty?
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true
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```
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Given the following meals
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```shell
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> echo [[meal size]; [arepa small] [taco '']]
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═══╦═══════╦═══════
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# ║ meal ║ size
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═══╬═══════╬═══════
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0 ║ arepa ║ small
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1 ║ taco ║
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═══╩═══════╩═══════
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```
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Show the empty contents
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```shell
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> echo [[meal size]; [arepa small] [taco '']] | empty? meal size
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═══╦═══════╦═══════
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# ║ meal ║ size
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═══╬═══════╬═══════
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0 ║ false ║ false
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1 ║ false ║ true
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═══╩═══════╩═══════
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```
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Let's assume we have a report of totals per day. For simplicity we show just for three days `2020/04/16`, `2020/07/10`, and `2020/11/16`. Like so
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```shell
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> echo [[2020/04/16 2020/07/10 2020/11/16]; ['' 27 37]]
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═══╦════════════╦════════════╦════════════
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# ║ 2020/04/16 ║ 2020/07/10 ║ 2020/11/16
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═══╬════════════╬════════════╬════════════
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0 ║ ║ 27 ║ 37
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═══╩════════════╩════════════╩════════════
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```
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In the future, the report now has many totals logged per day. In this example, we have 1 total for the day `2020/07/10` and `2020/11/16` like so
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```shell
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> echo [[2020/04/16 2020/07/10 2020/11/16]; ['' [27] [37]]]
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═══╦════════════╦════════════════╦════════════════
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# ║ 2020/04/16 ║ 2020/07/10 ║ 2020/11/16
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═══╬════════════╬════════════════╬════════════════
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0 ║ ║ [table 1 rows] ║ [table 1 rows]
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═══╩════════════╩════════════════╩════════════════
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```
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We want to add two totals (numbers `33` and `37`) for the day `2020/04/16`
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Set a table with two numbers for the empty column
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```shell
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> echo [[2020/04/16 2020/07/10 2020/11/16]; ['' [27] [37]]] | empty? 2020/04/16 { [33 37] }
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═══╦════════════════╦════════════════╦════════════════
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# ║ 2020/04/16 ║ 2020/07/10 ║ 2020/11/16
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═══╬════════════════╬════════════════╬════════════════
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0 ║ [table 2 rows] ║ [table 1 rows] ║ [table 1 rows]
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═══╩════════════════╩════════════════╩════════════════
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```
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Checking all the numbers
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```shell
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> echo [[2020/04/16 2020/07/10 2020/11/16]; ['' [27] [37]]] | empty? 2020/04/16 { [33 37] } | pivot _ totals | get totals
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═══╦════
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0 ║ 33
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1 ║ 37
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2 ║ 27
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3 ║ 37
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═══╩════
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``` |