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目录
R语言第二章数据处理⑥dplyr包(1)列选取
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注意：所有代码都将作为管道的一部分呈现，即使它们中的任何一个都不是完整的管道。 在某些情况下，我添加了一个glimpse()语句，允许您查看输出tibble中选择的列，而不必每次都打印所有数据。
数据集
library(tidyverse)
#built-in R dataset
glimpse(msleep)
## Observations: 83
## Variables: 11
## $ name "Cheetah", "Owl monkey", "Mountain beaver", "Grea...
## $ genus "Acinonyx", "Aotus", "Aplodontia", "Blarina", "Bo...
## $ vore "carni", "omni", "herbi", "omni", "herbi", "herbi...
## $ order "Carnivora", "Primates", "Rodentia", "Soricomorph...
## $ conservation "lc", NA, "nt", "lc", "domesticated", NA, "vu", N...
## $ sleep_total 12.1, 17.0, 14.4, 14.9, 4.0, 14.4, 8.7, 7.0, 10.1...
## $ sleep_rem NA, 1.8, 2.4, 2.3, 0.7, 2.2, 1.4, NA, 2.9, NA, 0....
## $ sleep_cycle NA, NA, NA, 0.1333333, 0.6666667, 0.7666667, 0.38...
## $ awake 11.9, 7.0, 9.6, 9.1, 20.0, 9.6, 15.3, 17.0, 13.9,...
## $ brainwt NA, 0.01550, NA, 0.00029, 0.42300, NA, NA, NA, 0....
## $ bodywt 50.000, 0.480, 1.350, 0.019, 600.000, 3.850, 20.4...
选取列
选取列：基础部分
如果目的是选择其中几列，只需在select语句中添加列的名称即可。 添加它们的顺序将决定它们在output中的显示顺序。
msleep %>%
select(name, genus, sleep_total, awake) %>%
glimpse()
## Observations: 83
## Variables: 4
## $ name "Cheetah", "Owl monkey", "Mountain beaver", "Great...
## $ genus "Acinonyx", "Aotus", "Aplodontia", "Blarina", "Bos...
## $ sleep_total 12.1, 17.0, 14.4, 14.9, 4.0, 14.4, 8.7, 7.0, 10.1,...
## $ awake 11.9, 7.0, 9.6, 9.1, 20.0, 9.6, 15.3, 17.0, 13.9, ...
如果你想添加很多列，可以通过使用：提高工作效率，取消选择甚至取消选择列并重新添加它来进行选择。同时可以请使用start_col：end_col语法选择某些列：
msleep %>%
select(name:order, sleep_total:sleep_cycle) %>%
glimpse
## Observations: 83
## Variables: 7
## $ name "Cheetah", "Owl monkey", "Mountain beaver", "Great...
## $ genus "Acinonyx", "Aotus", "Aplodontia", "Blarina", "Bos...
## $ vore "carni", "omni", "herbi", "omni", "herbi", "herbi"...
## $ order "Carnivora", "Primates", "Rodentia", "Soricomorpha...
## $ sleep_total 12.1, 17.0, 14.4, 14.9, 4.0, 14.4, 8.7, 7.0, 10.1,...
## $ sleep_rem NA, 1.8, 2.4, 2.3, 0.7, 2.2, 1.4, NA, 2.9, NA, 0.6...
## $ sleep_cycle NA, NA, NA, 0.1333333, 0.6666667, 0.7666667, 0.383...
另一种方法是通过在列名称前添加减号来取消选择列。 还可以通过此操作取消选择某些列。
msleep %>%
select(-conservation, -(sleep_total:awake)) %>%
glimpse
## Observations: 83
## Variables: 6
## $ name "Cheetah", "Owl monkey", "Mountain beaver", "Greater s...
## $ genus "Acinonyx", "Aotus", "Aplodontia", "Blarina", "Bos", "...
## $ vore "carni", "omni", "herbi", "omni", "herbi", "herbi", "c...
## $ order "Carnivora", "Primates", "Rodentia", "Soricomorpha", "...
## $ brainwt NA, 0.01550, NA, 0.00029, 0.42300, NA, NA, NA, 0.07000...
## $ bodywt 50.000, 0.480, 1.350, 0.019, 600.000, 3.850, 20.490, 0...
甚至可以取消所有列，然后重新添加其中某列。下面的示例代码取消选择从name到awake的所有列，但重新添加列'conservation'，即使它是取消选择的列的一部分。 但这只适用于在同一select()语句中。
msleep %>%
select(-(name:awake), conservation) %>%
glimpse
## Observations: 83
## Variables: 3
## $ brainwt NA, 0.01550, NA, 0.00029, 0.42300, NA, NA, NA, 0....
## $ bodywt 50.000, 0.480, 1.350, 0.019, 600.000, 3.850, 20.4...
## $ conservation "lc", NA, "nt", "lc", "domesticated", NA, "vu", N...
根据列名特点选择列
如果你有很多具有类似列名的列，你可以通过在select语句中添加starts_with()，ends_with()或contains()来使用匹配。
msleep %>%
select(name, starts_with("sleep")) %>%
glimpse
## Observations: 83
## Variables: 4
## $ name "Cheetah", "Owl monkey", "Mountain beaver", "Great...
## $ sleep_total 12.1, 17.0, 14.4, 14.9, 4.0, 14.4, 8.7, 7.0, 10.1,...
## $ sleep_rem NA, 1.8, 2.4, 2.3, 0.7, 2.2, 1.4, NA, 2.9, NA, 0.6...
## $ sleep_cycle NA, NA, NA, 0.1333333, 0.6666667, 0.7666667, 0.383...
msleep %>%
select(contains("eep"), ends_with("wt")) %>%
glimpse
## Observations: 83
## Variables: 5
## $ sleep_total 12.1, 17.0, 14.4, 14.9, 4.0, 14.4, 8.7, 7.0, 10.1,...
## $ sleep_rem NA, 1.8, 2.4, 2.3, 0.7, 2.2, 1.4, NA, 2.9, NA, 0.6...
## $ sleep_cycle NA, NA, NA, 0.1333333, 0.6666667, 0.7666667, 0.383...
## $ brainwt NA, 0.01550, NA, 0.00029, 0.42300, NA, NA, NA, 0.0...
## $ bodywt 50.000, 0.480, 1.350, 0.019, 600.000, 3.850, 20.49...
根据正则表达式选择列
以上的辅助函数都是使用精确的模式匹配。 如果你有列名模式并不精确相同，你可以在matches()中使用任何正则表达式。下面的示例代码将添加任何包含“o”的列，后跟一个或多个其他字母，以及“er”。
#selecting based on regex
msleep %>%
select(matches("o.+er")) %>%
glimpse
## Observations: 83
## Variables: 2
## $ order "Carnivora", "Primates", "Rodentia", "Soricomorph...
## $ conservation "lc", NA, "nt", "lc", "domesticated", NA, "vu", N...
根据预先确定的列名选择列
还有另一个选项可以避免连续重新输入列名：one_of()。 您可以预先设置列名，然后在select()语句中通过将它们包装在one_of()中或使用!!运算符来引用它们。
classification
msleep %>%
select(!!classification)
## # A tibble: 83 x 5
## name genus vore order conservation
##
## 1 Cheetah Acinonyx carni Carnivora lc
## 2 Owl monkey Aotus omni Primates
## 3 Mountain beaver Aplodontia herbi Rodentia nt
## 4 Greater short-tailed shrew Blarina omni Soricomorpha lc
## 5 Cow Bos herbi Artiodactyla domesticated
## 6 Three-toed sloth Bradypus herbi Pilosa
## 7 Northern fur seal Callorhinus carni Carnivora vu
## 8 Vesper mouse Calomys Rodentia
## 9 Dog Canis carni Carnivora domesticated
## 10 Roe deer Capreolus herbi Artiodactyla lc
## # ... with 73 more rows