[GRASS-user] update column w/ output from bash function

[Moritz Lennert]

Le 12 janvier 2017 17:49:12 GMT+01:00, Ken Mankoff <mankoff at gmail.com> a écrit :
>Hi Helmut,
>
>I misspoke and the data column I'm working with is not Julian Day (JD)
>but Day of Year (DOY). I looked at the SQL datetime functions and can't
>find a way to convert DOY to YYY-MM-DD. Can you help with this?
>
>Also, you are correct, these modules do not work with bash. Is there
>any way to populate a column with something other than SQL? I think SQL
>is Turing complete and therefore can be used for arbitrarily complex
>functions, but it doesn't seem like the right tool in this case. There
>are simple bash commands that can generate the data, but I have no way
>to get that data into the column without a for loop, which is
>computationally slow. My current solution is:
>
># extract the category (unique) and the DOY column (1 and 13)
>for cat_DOY in $(db.select table=CTD_2015| cut -d"|" -f1,13); do
>    # separate into category and DOY
>    cat=$(echo $cat_DOY | cut -d"|" -f1)
>    DOY=$(echo $cat_DOY | cut -d"|" -f2)
>    YMD=$(doy2ymd 2015 ${DOY})
>  v.db.update map=CTD_2015 column=YMD where="cat = ${cat}" value=${YMD}
>done

It should be possible to do this directly in SQL, but if not you might want to modify your script to write complete SQL UPDATE statements for each cat_DOY to a file (instead of the v.db.update calls) and then, once the loop is done, feed that file to db.execute. This will probably be faster.

Moritz



>
>Thanks,
>
>  -k.
>
>On 2017-01-12 at 14:56, Helmut Kudrnovsky <hellik at web.de> wrote:
>> Helmut Kudrnovsky wrote
>>>>Neither db.execute nor db.select appear to work with arbitrary bash
>> commands.
>>> 
>>> AFAIK these modules need a SQL statement, not a bash command; e.g.
>[1]:
>>> db.execute - Executes any SQL statement.
>>> 
>>> 
>>> [1] https://grass.osgeo.org/grass73/manuals/db.execute.html
>>
>> there are some sqlite Date And Time Functions:
>> https://www.sqlite.org/lang_datefunc.html
>>
>>
>>
>> -----
>> best regards
>> Helmut
>
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