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扩展App Inventor：具有多点触控和手势检测功能 · App Inventor 2 中文网
...s detection, such as two-finger rotation, and user-defined custom gestures by building extension components. Our paper illustrates the implementation of components, sample usage of the components and how they will help novices building apps involving gesture recognition.
KEYWORDS
System, Computer ...
What does .SD stand for in data.table in R
...elp you see what .SD is:
DT[ , .SD[ , paste(x, v, sep="", collapse="_")], by=y]
# y V1
# 1: 1 a1_b3_c5
# 2: 3 a2_b4_c6
Basically, the by=y statement breaks the original data.table into these two sub-data.tables
DT[ , print(.SD), by=y]
# <1st sub-data.table, called '.SD' while it's be...
SQL selecting rows by most recent date
...
You can use a GROUP BY to group items by type and id. Then you can use the MAX() Aggregate function to get the most recent service month. The below returns a result set with ChargeId, ChargeType, and MostRecentServiceMonth
SELECT
CHARGEID,
...
Postgres: Distinct but only for one column
... to order:
select distinct on (name)
name, col1, col2
from names
order by name, col1
Will return the first row when ordered by col1.
distinct on:
SELECT DISTINCT ON ( expression [, ...] ) keeps only the first row of each set of rows where the given expressions evaluate to equal. The DISTINCT O...
Sort a list by multiple attributes?
...swered Nov 20 '10 at 15:32
Mark ByersMark Byers
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扩展App Inventor：具有多点触控和手势检测功能 · App Inventor 2 中文网
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扩展App Inventor：具有多点触控和手势检测功能
« ...
What are the rules about using an underscore in a C++ identifier?
...on macros:
identifiers beginning with an underscore followed immediately by an uppercase letter
identifiers containing adjacent underscores (or "double underscore")
Reserved in the global namespace:
identifiers beginning with an underscore
Also, everything in the std namespace is reserved. (Yo...
How do I import CSV file into a MySQL table?
... database:
mysqlimport --ignore-lines=1 \
--fields-terminated-by=, \
--local -u root \
-p Database \
TableName.csv
I found it at http://chriseiffel.com/everything-linux/how-to-import-a-large-csv-file-to-mysql/
To make the delimiter a tab, use --fi...
lexers vs parsers
.... But it
has to be of symbols which are atomic for the language
understood by parser/lexer.
Symbols for the lexer: ASCII characters.
Symbols for the parser: the particular tokens, which are terminal symbols of their grammar.
They analyse these symbols and try to match them with the grammar of the l...
How to sort a dataframe by multiple column(s)
I want to sort a data.frame by multiple columns. For example, with the data.frame below I would like to sort by column z (descending) then by column b (ascending):
...