R中的[]包只允许我使用&&运算符选择一次使用一个简单逻辑测试的行。即使逻辑上等效的||语句按预期工作，我也无法使用ifelse或ifelse运算符。这种限制有什么好的理由吗？它有简单，更冗长的解决方法，如&&（以及模拟R version 3.3.2 (2016-10-31) -- "Sincere Pumpkin Patch"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-unknown-cygwin (64-bit)
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> library(data.table)
data.table 1.10.4
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> dt <- data.table(a=1:6, b=11:16) # Make a sample data table.
> dt # Print the data table, for easy reference.
a b
1: 1 11
2: 2 12
3: 3 13
4: 4 14
5: 5 15
6: 6 16
> dt[a >= 3] # A single logical test works fine.
a b
1: 3 13
2: 4 14
3: 5 15
4: 6 16
> dt[((a >= 3) && (b <= 15))] # Conjunction with && returns zero rows.
Empty data.table (0 rows) of 2 cols: a,b
> dt[ifelse(a >= 3, b <= 15, FALSE)] # The equivalent ifelse call works.
a b
1: 3 13
2: 4 14
3: 5 15
> dt[((a <= 2) || (b >= 15))] # Disjunction with || returns every row.
a b
1: 1 11
2: 2 12
3: 3 13
4: 4 14
5: 5 15
6: 6 16
> dt[ifelse(a <= 2, TRUE, b >= 15)] # The equivalent ifelse call works.
a b
1: 1 11
2: 2 12
3: 5 15
4: 6 16
的方法链接），但它仍然令人恼火。
这是一个说明性终端会议的成绩单。
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