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How do I delete rows in a data frame?
... :
mydata[-seq(2, nrow(mydata), by = 2) , ]
Or if you want to subset by selecting odd numbers:
mydata[which(1:nrow(mydata) %% 2 == 1) , ]
Or if you want to subset by selecting odd numbers, version 2:
mydata[which(1:nrow(mydata) %% 2 != 0) , ]
Or if you want to subset by filtering even numbe...
Unable to cast object of type 'System.DBNull' to type 'System.String`
... even both. If the WHERE does not match any row, you'll get a null, if the selected row has NULL in that column, the return value is System.DBNull.
– Alexander
May 27 '14 at 7:52
...
Pass a data.frame column name to a function
...(x[,column])
}
fun1(df, "B", max)
Alternatively, using [[ also works for selecting a single column at a time:
df <- data.frame(A=1:10, B=2:11, C=3:12)
fun1 <- function(x, column){
max(x[[column]])
}
fun1(df, "B")
...
how to ignore namespaces with XPath
...
You can use the local-name() XPath function. Instead of selecting a node like
/path/to/x:somenode
you can select all nodes and filter for the one with the correct local name:
/path/to/*[local-name() = 'somenode']
...
Eclipse: Java, see where class is used
Is there a way in Eclipse to select a Java class, and then bring up a list of all Java files where that class is used within a project?
...
ALTER DATABASE failed because a lock could not be placed on database
... for a couple of minutes)
CREATE DATABASE TESTING123
GO
USE TESTING123;
SELECT NEWID() AS X INTO FOO
FROM sys.objects s1,sys.objects s2,sys.objects s3,sys.objects s4 ,sys.objects s5 ,sys.objects s6
Connections 2 and 3
set lock_timeout 5;
ALTER DATABASE TESTING123 SET SINGLE_USER WITH ROLLBACK...
Loading local JSON file
...
If you want to let the user select the local json file (anywhere on the filesystem), then the following solution works.
It uses uses FileReader and JSON.parser (and no jquery).
<html>
<body>
<form id="jsonFile" name="jsonFile" enctype=...
如何选择机器学习算法 - 大数据 & AI - 清泛网移动版 - 专注C/C++及内核技术
...aking sure to try different parameters within each algorithm as well), and select the best one by cross-validation. But if you’re simply looking for a “good enough” algorithm for your problem, or a place to start, here are some general guidelines I’ve found to work well over the year...
How to use JNDI DataSource provided by Tomcat in Spring?
..."7200000"
testOnBorrow="true"
validationQuery="select 1"
/>
</GlobalNamingResources>
And reference the JNDI resource from Tomcat's web context.xml like this:
<ResourceLink name="jdbc/DatabaseName"
global="jdbc/DatabaseName"
type="javax...
Bash: Strip trailing linebreak from output
...ine character you want to remove, you can use 'head' from GNU coreutils to select everything except the last byte. This should be quite quick:
head -c -1 log.txt
Also, for completeness, you can quickly check where your newline (or other special) characters are in your file using 'cat' and the 'sh...