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How do I combine two data-frames based on two columns? [duplicate]
...final example given in the documentation:
x <- data.frame(k1=c(NA,NA,3,4,5), k2=c(1,NA,NA,4,5), data=1:5)
y <- data.frame(k1=c(NA,2,NA,4,5), k2=c(NA,NA,3,4,5), data=1:5)
merge(x, y, by=c("k1","k2")) # NA's match
This example was meant to demonstrate the use of incomparables, but it illustra...
What does “static” mean in C?
...= 15, sa = 20
a = 15, sa = 25
a = 15, sa = 30
a = 15, sa = 35
a = 15, sa = 40
a = 15, sa = 45
a = 15, sa = 50
a = 15, sa = 55
a = 15, sa = 60
This is useful for cases where a function needs to keep some state between invocations, and you don't want to use global variables. Beware, however, this fe...
What is size_t in C?
...
471
From Wikipedia:
According to the 1999 ISO C standard
(C99), size_t is an unsigned intege...
What is the difference between C++ and Visual C++? [duplicate]
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edited Oct 4 '18 at 16:11
Joaquin Marcher
17322 silver badges1212 bronze badges
answered ...
Why doesn't C have unsigned floats?
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114
Why C++ doesn't have support for unsigned floats is because there is no equivalent machine code ...
What is the difference between ${var}, “$var”, and “${var}” in the Bash shell?
...ariable is unset or not set. REF: github.com/koalaman/shellcheck/wiki/SC2154
– Nam Nguyen
Apr 7 '15 at 4:32
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How to prevent moment.js from loading locales with webpack?
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Zeeshan Hassan Memon
6,65433 gold badges3434 silver badges5050 bronze badges
answered Aug 21 '14 at 12:09
Tobias K.Tobias K.
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Reorder levels of a factor without changing order of values
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Use the levels argument of factor:
df <- data.frame(f = 1:4, g = letters[1:4])
df
# f g
# 1 1 a
# 2 2 b
# 3 3 c
# 4 4 d
levels(df$g)
# [1] "a" "b" "c" "d"
df$g <- factor(df$g, levels = letters[4:1])
# levels(df$g)
# [1] "d" "c" "b" "a"
df
# f g
# 1 1 a
# 2 2 b
# 3 3 c
# 4 ...