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Select first 4 rows of a data.frame in R
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You can use the "index" answer pointed out elsewhere. In this situation I normally use the slice function in dplyr. (Behavior depends on the grouping.)
– Eduardo Leoni
May 28 '18 at 21:16
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How is this fibonacci-function memoized?
... passed in and this is easy to verify. The list is a constant that is then indexed into. It is, of course, a constant that is lazily evaluated, so your program does not try to get the whole (infinite) list immediately. Since it's a constant, it can be shared across the function calls.
It's memoized...
Error installing libv8: ERROR: Failed to build gem native extension
...rrupted. I remove the whole cache folder and re-run bundle install --full-index --deployment --without development test postgres aws. Works.
– Nick Dong
Mar 2 '16 at 11:11
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Java SE 6 vs. JRE 1.6 vs. JDK 1.6 - What do these mean?
...ava SE Downloads": http://www.oracle.com/technetwork/java/javase/downloads/index.html
Click "JDK Download" and visit "Java SE Development Kit 7 Downloads": http://www.oracle.com/technetwork/java/javase/downloads/java-se-jdk-7-download-432154.html (note that following the link from step #1 will take ...
How do I replace NA values with zeros in an R dataframe?
...ring of other helpful tidyverse replacement approaches
Locationally:
index mutate_at(c(5:10), ~replace(., is.na(.), 0))
direct reference mutate_at(vars(var5:var10), ~replace(., is.na(.), 0))
fixed match mutate_at(vars(contains("1")), ~replace(., is.na(.), 0))
or in place of contains(), ...
SQL “select where not in subquery” returns no results
...mortech's answer and @rexem's comments.
If either Table1 or Table2 is not indexed on commonID, you get a table scan but @patmortech's query is still twice as fast (for a 100K row master table).
If neither are indexed on commonID, you get two table scans and the difference is negligible.
If both a...
get dictionary key by value
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types.Values.ToList().IndexOf("one");
Values.ToList() converts your dictionary values into a List of objects.
IndexOf("one") searches your new List looking for "one" and returns the Index which would match the index of the Key/Value pair in the ...
Why does 'git commit' not save my changes?
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Maybe an obvious thing, but...
If you have problem with the index, use git-gui. You get a very good view how the index (staging area) actually works.
Another source of information that helped me understand the index was Scott Chacons "Getting Git" page 259 and forward.
I started off...
C# equivalent to Java's charAt()?
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You can index into a string in C# like an array, and you get the character at that index.
Example:
In Java, you would say
str.charAt(8);
In C#, you would say
str[8];
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git: Switch branch and ignore any changes without committing
...inor changes) or
checkout -f (When switching branches, proceed even if the index or the working tree differs from HEAD. This is used to throw away local changes. )
Or, more recently:
With Git 2.23 (August 2019) and the new command git switch:
git switch -f <branch-name>
(-f is short for --...