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Remove columns from dataframe where ALL values are NA
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dplyr now has a select_if verb that may be helpful here:
library(dplyr)
temp <- data.frame(x = 1:5, y = c(1,2,NA,4, 5), z = rep(NA, 5))
not_all_na <- function(x) any(!is.na(x))
not_any_na <- function(x) all(!is.na(x))
> temp
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If table exists drop table then create it, if it does not exist just create it
...up the old table,
obviously.
Wrapping all statements with something like SELECT GET_LOCK('__upgrade', -1); ... DO RELEASE_LOCK('__upgrade'); allows to just invoke all statements sequentially without error checking, but I don't think it's a good idea: complexity increases and locking functions in M...
How to log PostgreSQL queries?
...ement = 'all'
#logging_collector = off to logging_collector = on
Optional: SELECT set_config('log_statement', 'all', true);
sudo /etc/init.d/postgresql restart or sudo service postgresql restart
Fire query in postgresql select 2+2
Find current log in /var/lib/pgsql/9.2/data/pg_log/
The log files t...
内存优化总结:ptmalloc、tcmalloc和jemalloc - 操作系统(内核) - 清泛网 - ...
... 总共32个vcpu。 16个table，每个5M row。
OLTP_RO测试包含5个select查询：select_ranges, select_order_ranges, select_distinct_ranges, select_sum_ranges,
可以看到在多核心或者多线程的场景下， jemalloc和tcmalloc带来的tps增加非常明显。
参考资料
glibc...
jQuery: Check if div with certain class name exists
...presumably because it changes the native features jQuery can use to do the selection. Here's a test case where the div exists, and here's one where it doesn't exist.
– T.J. Crowder
Apr 26 '11 at 6:10
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How to show the last queries executed on MySQL?
...the result in this way, but parameters are present by question mark, e.g., select foo from bar where x=?. How can I get the complete query?
– petertc
Nov 4 '15 at 5:52
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Is there a performance difference between CTE , Sub-Query, Temporary Table or Table Variable?
...ur question. If you click on the link you will see the reasons those users selected.
– Aaron Bertrand
Jun 23 '12 at 17:13
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How to verify an XPath expression in Chrome Developers tool or Firefox's Firebug?
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In "Elements" panel, press Ctrl+F
In the search box, type in XPath or CSS Selector, if elements are found, they will be highlighted in yellow.
Firefox (since version 75)
Since FF 75 it's possible to use raw xpath query without evaluation xpath expressions, see documentation for more info.
Fir...
How can I match on an attribute that contains a certain string?
I am having a problem selecting nodes by attribute when the attributes contains more than one word. For example:
10 Answer...
Java project in Eclipse: The type java.lang.Object cannot be resolved. It is indirectly referenced f
...teps could help:
Right-click on project » Properties » Java Build Path
Select Libraries tab
Find the JRE System Library and remove it
Click Add Library... button at right side » Add the JRE System Library (Workspace default JRE)
...