1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
|
--- status: Rewritten July 2020
--- author(s): Mahrud
--- notes:
-- TODO: bring all uses as synopses under this node
doc ///
Key
select
Headline
select from a list, hash table, or string
SeeAlso
partition
///
doc ///
Key
(select, String, String, String)
(select, String, String)
[(select, String, String), POSIX]
[(select, String, String, String), POSIX]
Headline
select and reformat substrings matching a regular expression
Usage
select(re, replacement, str)
select(re, str)
Inputs
re:String
a @TO2 {"regular expressions", "regular expression"}@ describing a pattern
replacement:String
following the @TO2 {"regular expressions", "formatting syntax"}@
str:String
a subject string to be searched
POSIX=>Boolean
if true, interpret the @TT "re"@ using the POSIX Extended flavor, otherwise the Perl flavor
Outputs
:List
of mutually exclusive substrings of @TT "str"@ matching the pattern @TT "re"@;
if @TT "replacement"@ is given, the matching substrings are formatted based on it.
Description
Text
For an introduction to regular expressions, see @TO "regular expressions"@.
Example
select("[[:alpha:]]+", "Dog, cat, and deer.")
select("^.*$", "ABC\nDEF\r\nGHI")
Text
The @TT "replacement"@ string may contain @TO2 {"regular expressions", "formatting syntax"}@
such as backreferences @TT "$1"@ or @TT "\\\\1"@, which will be replaced by the string matching
the corresponding parenthesized subexpression of @TT "re"@.
Example
select("([a-zA-Z]+);", "$1", "Dog; cat, deer;")
Text
Special operators such as the lowercase operator @TT "\\\\L"@ may also be used to manipulate the
replacement substring.
Example
select("([a-zA-Z]+);", "\\L$1", "Dog; cat, deer;")
Text
Lookaheads and lookbehinds can be used to precisely control the regular expression matches.
Example
s = "catfish cats dogs";
select("cat(?!fish)s?", s)
select("\\w+(?=s\\b)", s)
s = "goldfish swordfish catfish catdog";
select("\\w+(?=fish)", s)
select("(?<=cat)\\w+", s)
Text
The @TT "POSIX => true"@ option can be used to specify the POSIX Extended flavor for the regular
expression used to match. Note that only the Perl flavor allows the use of lookaheads and lookbehinds.
SeeAlso
"regular expressions"
"strings and nets"
regex
separate
(replace, String, String, String)
///
doc ///
Node
Key
(select, BasicList, Type)
Headline
select elements of a given type in a list
Usage
select(L, T)
Inputs
L:BasicList
T:Type
Outputs
:BasicList
containing elements of @TT "L"@ whose class inherits from type @TT "T"@
Description
Text
The order of the elements in the result will be the same as in the original list @TT "L"@,
and the class of the result will be the same as the class of @TT "L"@.
Example
select({1,"2",3.14,4+5*ii}, ZZ)
select([1,"2",3.14,4+5*ii], RR)
SeeAlso
(select, BasicList, Function)
///
document {
Key => (select,ZZ,BasicList,Function),
Headline => "select a limited number of elements from a list",
Usage => "select(n,v,f)",
Inputs => { "n", "v", "f" => {"returning either ", TO "true", " or ", TO "false"}},
Outputs => {
{"a list containing at most ", TT "n", " elements of the list ", TT "v", "
that yield ", TT "true", " when the function ", TT "f", " is applied."}
},
"The order of the elements in the result will be the same as
in the original list ", TT "v", ".",
EXAMPLE {
///select(4,0..10,even)///
},
SeeAlso => {(select,BasicList,Function),partition}
}
document {
Key => (select,HashTable,Function),
Headline => "select part of a hash table",
Usage => "select(v,f)",
Inputs => { "v", "f" => {"returning either ", TO "true", " or ", TO "false"} },
Outputs => {
{"whose pairs are those key-value pairs ", TT "(k,w)", " of the hash table ", TT "v", " that
yield ", TT "true", " when the function ", TT "f", " is applied to the value ", TT "w", "."}
},
"The hash table ", TT "v", " should be immutable: to scan the values in a mutable hash
table, use ", TT "scan(values x, f)", ".",
EXAMPLE {
"x = new HashTable from { x => 1, y => 2, z => 3 }",
"select(x,odd)"
},
SeeAlso => {partition}
}
document {
Key => (select,ZZ,HashTable,Function),
Headline => "select a limited number of pairs from a hash table",
Usage => "select(n,v,f)",
Inputs => { "n", "v", "f" => {"returning either ", TO "true", " or ", TO "false"} },
Outputs => {
{"whose pairs are those key-value pairs of the hash table ", TT "v", " that
yield ", TT "true", " when the function ", TT "f", " is applied to the value,
except that at most ", TT "n", " pairs will be selected"}
},
"The hash table ", TT "v", " should be immutable: to scan the values in a mutable hash
table, use ", TT "scan(values x, f)", ".",
EXAMPLE {
"x = new HashTable from { x => 1, y => 2, z => 3 }",
"select(1,x,odd)"
},
SeeAlso => {(select,HashTable,Function), partition}
}
document {
Key => (select,BasicList,Function),
Headline => "select elements from a list",
Usage => "select(v,f)",
Inputs => { "v", "f" => {"returning either ", TO "true", " or ", TO "false"} },
Outputs => {
{"a list of those elements of the list ", TT "v", " that yield ", TT "true", " when the function ", TT "f", " is applied"}
},
"The order of the elements in the result will be the same as
in the original list ", TT "v", ", and the class of the result
will be the same as the class of ", TT "v", ".",
EXAMPLE {
"select({1,2,3,4,5}, odd)",
"select([1,2,3,4,5], odd)",
},
SeeAlso => {(select,ZZ,BasicList,Function), partition, positions}
}
document {
Key => (select,ZZ,Function),
Headline => "select integers",
Usage => "select(n,f)",
Inputs => { "n", "f" => {"returning either ", TO "true", " or ", TO "false"} },
Outputs => {
{"a list of those natural numbers ", TT "i", " less than ", TT "n", " that yield
", TT "true", " when the function ", TT "f", " is applied"}
},
EXAMPLE {
"select(20, odd)",
"select(20, even)",
},
SeeAlso => {(select,ZZ,BasicList,Function), partition, positions}
}
doc ///
Key
(select, Thing, Function)
Headline
select elements from an object with an iterator
Usage
select(x, f)
Inputs
x:Thing -- an instance of a class with the @TO iterator@ method installed
f:Function -- returning either @TO true@ or @TO false@
Outputs
:Iterator
Description
Text
Suppose @TT "x"@ is an instance of a class with the @TO iterator@ method
installed, e.g., a string, and suppose @TT "iter"@ is the output of
@TT "iterator x"@. Then a new @TO Iterator@ object is returned
whose @TO next@ method returns the next output of @TT "next iter"@
for which @TT "f next iter" @ is true, unless @TT "next iter"@ returns
@TO StopIteration@, in which case this new iterator does the same.
Example
selectiter = select("foo", i -> i == "o")
next selectiter
next selectiter
next selectiter
SeeAlso
iterator
Iterator
next
StopIteration
(apply, Thing, Function)
///
|
