For example I loaded a module, and there is a table in this module with name "Table1". In the main file I have a table which I want to be the exact same copy of "Table1".
So how can I do it, if I have only a name of that table.
When I am trying to do it like this
str = "Table1"
t = str
I obviously get a string instead of table, so how can I get a table content that table content? What I want is to able somehow make this line of code
t = 'Table1'
be equvalent to this one
t = Table1
If str is the name of a global variable, use _G[str] to get its value.
Tables in Lua are a very flexible and important datatype. So much, that even modules are tables. If you know, that there is a table by a given name in the module, and you have it's name in a variable, just use the [] operator to get the table:
tablename = 'Table1' -- you get this from somewhere, assuming it's not fixed
require 'mymodule'
t = mymodule[tablename]
However, this is not a very good approach, because it assumes that you "know" that the module contains a table by the given name. You can always design modules that will export the table by a given standard name (which does not change):
require 'mymodule'
t = mymodule.Table1 -- equivalent to mymodule['Table1']
Related
In python3 and postgresql12, is there a safety difference between parametizing SQL queries the "proper" way or just escaping potentially dangerous content using psycopg2.quote_ident()?
For example, consider these two options.
Option 1:
name = get_unsafe_input_from_web_form()
cursor.execute("SELECT * FROM students WHERE name = %s;", (name,))
Option 2:
from psycopg2.extensions import quote_ident
name = get_unsafe_input_from_web_form()
cursor.execute(f"SELECT * FROM students WHERE name = {quote_ident(name, cursor)};"
The documentation is not particularly explicit. Is Option 2 totally equivalent in terms of safety against injection attacks?
quote_ident() would be the wrong thing to use, as it is for identifiers e.g table, column names. You would want quote_literal() which does not exist in psycopg2.extensions. I would stick with the first option, but using the psycopg2.sql module:
https://www.psycopg.org/docs/sql.html
Safety-wise, both parameterized queries and quote_ident can safely handle untrusted input and will not open you to SQL injection issues. But you can't use quote_ident for values as you're trying to do in your example. The string you're passing to cursor.execute() will end up being (for name foobar) SELECT * FROM students WHERE name = "foobar";, which will try to find rows where the name column is equal to the foobar column, not where name is equal to the string 'foobar'.
An Excel table as data source may contain error values (#NA, #DIV/0), which could disturbe later some steps during the transformation process in Power Query.
Depending of the following steps, we may get no output but an error. So how to handle this cases?
I found two standard steps in Power Query to catch them:
Remove errors (UI: Home/Remove Rows/Remove Errors) -> all rows with an error will be removed
Replace error values (UI: Transform/Replace Errors) -> the columns have first to be selected for performing this operations.
The first possibility is not a solution for me, since I want to keep the rows and just replace the error values.
In my case, my data table will change over the time, means the column name may change (e.g. years), or new columns appear. So the second possibility is too static, since I do not want to change the script each time.
So I've tried to get a dynamic way to clean all columns, indepent from the column names (and number of columns). It replaces the errors by a null value.
let
Source = Excel.CurrentWorkbook(){[Name="Tabelle1"]}[Content],
//Remove errors of all columns of the data source. ColumnName doesn't play any role
Cols = Table.ColumnNames(Source),
ColumnListWithParameter = Table.FromColumns({Cols, List.Repeat({""}, List.Count(Cols))}, {"ColName" as text, "ErrorHandling" as text}),
ParameterList = Table.ToRows(ColumnListWithParameter ),
ReplaceErrorSource = Table.ReplaceErrorValues(Source, ParameterList)
in
ReplaceErrorSource
Here the different three queries messages, after I've added two new column (with errors) to the source:
If anybody has another solution to make this kind of data cleaning, please write your post here.
let
src = Excel.CurrentWorkbook(){[Name="Tabelle1"]}[Content],
cols = Table.ColumnNames(src),
replace = Table.ReplaceErrorValues(src, List.Transform(cols, each {_, "!"}))
in
replace
Just for novices like me in Power Query
"!" could be any string as substitute for error values. I initially thought it was a wild card.
List.Transform(cols, each {_, "!"}) generates the list of error handling by column for the main funcion:
Table.ReplaceErrorValues(table_with errors, {{col1,error_str1},{col2,error_str2},{},{}, ...,{coln,error_strn}})
Nice elegant solution, Sergei
I have created a structure containing a few different fields. The fields contain data from a number of different subjects/participants.
At the beginning of the script I prompt the user to enter the "Subject number" like so:
prompt='Enter the subject number in the format SUB_n: ';
SUB=input(prompt,'s');
Example SUB_34 for the 34th subject.
I want to then name my structure such that it contains this string... i.e. I want the name of my structure to be SUB_34, e.g. SUB_34.field1. But I don't know how to do this.
I know that you can assign strings to a specific field name for example for structure S if I want field1 to be called z then
S=struct;
field1='z';
S.(field1);
works but it does not work for the structure name.
Can anyone help?
Thanks
Rather than creating structures named SUB_34 I would strongly recommend just using an array of structures instead and having the user simply input the subject number.
number = input('Subject Number')
S(number) = data_struct
Then you could simply find it again using:
subject = S(number);
If you really insist on it, you could use the method proposed in the comment by #Sembei using eval to get the struct. You really should not do this though
S = eval([SUB, ';']);
Or to set the structure
eval([SUB, ' = mydata;']);
One (of many) reasons not to do this is that I could enter the following at your prompt:
>> prompt = 'Enter the subject number in the format SUB_n: ';
>> SUB = input(prompt, 's');
>> eval([SUB, ' = mydata;']);
And I enter:
clear all; SUB_34
This would have the unforeseen consequence that it would remove all of your data since eval evaluates the input string as a command. Using eval on user input assumes that the user is never going to ever write something malformed or malicious, accidentally or otherwise.
I am attempting to write an algorithm that selects a specific reference standard (vector) as a function of temperature. The temperature values are stored in a structure ( procspectra(i).temperature ). My reference standards are stored in another structure ( standards.interp.zeroed.ClOxxx ) where xxx are numbers such as 200, 210, 220, etc. I have built the rounding construct and paste it below.
for i = 1:length(procspectra);
if mod(-procspectra(i).temperature,10) > mod(procspectra(i).temperature,10);
%if mod(-) > mod(+) round down, else round up
tempvector(i) = procspectra(i).temperature - mod(procspectra(i).temperature,10);
else
tempvector(i) = procspectra(i).temperature + mod(-procspectra(i).temperature,10);
end
clostd = strcat('standards.interp.zeroed.ClO',num2str(tempvector(i)));
end
This construct works well. Now, I have built a string which is identical to the name of the vector I want to invoke, but I'm uncertain how to actually call the vector given that this is encoded as a string. Ideally I want to do something within the for-loop like:
parameters(i).standards.ClOstandard = clostd
where I actually am assigning that parameter structure to be the same as the vector I have saved in the standards structure I have previously generated (and not just a string)
Could anyone help out?
Don't construct clostd like that (containing the full variable name), make it contain only the last field name instead:
clostd = ['ClO' num2str(tempvector(i))];
parameters(i).standards.ClOstandard = standards.interp.zeroed.(clostd);
This is the syntax of accessing a structure's field dynamically, using a string. So the following three are equivalent:
struc.Cl0123
struc.('Cl0123')
fieldn='Cl0123'; struc.(fieldn)
I need to import certain information from an Excel file into an Access DB and in order to do this, I am using DAO.
The user gets the excel source file from a system, he does not need to directly interact with it. This source file has 10 columns and I would need to retrieve only certain records from it.
I am using this to retrieve all the records:
Set destinationFile = CurrentDb
Set dbtmp = OpenDatabase(sourceFile, False, True, "Excel 8.0;")
DoEvents
Set rs = dbtmp.OpenRecordset("SELECT * FROM [EEX_Avail_Cap_ALL_DEU_D1_S_Y1$A1:J65536]")
My problem comes when I want to retrieve only certain records using a WHERE clause. The name of the field where I want to apply the clause is 'Date (UCT)' (remember that the user gets this source file from another system) and I can not get the WHERE clause to work on it. If I apply the WHERE clause on another field, whose name does not have ( ) or spaces, then it works. Example:
Set rs = dbtmp.OpenRecordset("SELECT * FROM [EEX_Avail_Cap_ALL_DEU_D1_S_Y1$A1:J65536] WHERE Other = 12925")
The previous instruction will retrieve only the number of records where the field Other has the value 12925.
Could anyone please tell me how can I achieve the same result but with a field name that has spaces and parenthesis i.e. 'Date (UCT)' ?
Thank you very much.
Octavio
Try enclosing the field name in square brackets:
SELECT * FROM [EEX_Avail_Cap_ALL_DEU_D1_S_Y1$A1:J65536] WHERE [Date (UCT)] = 12925
or if it's a date we are looking for:
SELECT * FROM [EEX_Avail_Cap_ALL_DEU_D1_S_Y1$A1:J65536] WHERE [Date (UCT)] = #02/14/13#;
To use date literal you must enclose it in # characters and write the date in MM/DD/YY format regardless of any regional settings on your machine