October 2017
Intermediate to advanced
480 pages
9h 49m
Japanese
Content preview from Rではじめるデータサイエンス
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260
16
章 ベクトル
整数と実数との相違は通常は重要ではありませんが、知っておくべき重要な相違点が 2 つありま
す。
●
実数は、限られたメモリ量では常に厳密な表現ができない浮動小数点数を表す。つまり、あらゆ
る実数は近似値と考える必要がある。例えば、2の平方根の2乗はどうなるだろうか。
x <- sqrt(2) ^ 2
x
#> [1] 2
x - 2
#> [1] 4.44e-16
浮動小数点数を扱うときにはこのような振る舞いが普通。ほとんどの計算に丸め誤差が含まれ
る。浮動小数点数の比較には、
==
ではなく、許容値を含んだ
dplyr::near()
を使うべきだ。
●
整数には特別な値
NA
が、実数には
NA
,
NaN
,
Inf
,
-Inf
という4つの特別な値がある。3つの特別
な値は割り算で作ることができる。
c(-1, 0, 1) / 0
#> [1] -Inf NaN Inf
これら の 特 別 な 値 の チ ェック に は
==
を 使 わ な い。 代 わりに ヘ ル パ ー 関 数
is.finite()
,
is.infinite()
,
is.nan()
を使う。
0 Inf NA NaN
is.finite()
〇
is.infinite()
〇
is.na()
〇 〇
is.nan()
〇
16.3.3
文字ベクトル
文字ベクトルは、各要素が文字列で、文字列にはどれだけでもデータが含まれるので、最も複雑
なアトミックベクトルです。
11章で文字列を扱う上で多くのことを既に学びました。本節では、文字列実装の基 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.