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Enumerate exercise subparts with letters

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Mine Çetinkaya-Rundel
2021-02-21 17:32:37 +00:00
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strings.Rmd
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@@ -314,10 +314,10 @@ For example, I'll search for `\bsum\b` to avoid matching `summarise`, `summary`,
2. Given the corpus of common words in `stringr::words`, create regular expressions that find all words that:
1. Start with "y".
2. End with "x"
3. Are exactly three letters long. (Don't cheat by using `str_length()`!)
4. Have seven letters or more.
a. Start with "y".
b. End with "x"
c. Are exactly three letters long. (Don't cheat by using `str_length()`!)
d. Have seven letters or more.
Since this list is long, you might want to use the `match` argument to `str_view()` to show only the matching or non-matching words.
@@ -360,14 +360,10 @@ str_view(c("grey", "gray"), "gr(e|a)y")
1. Create regular expressions to find all words that:
1. Start with a vowel.
2. That only contain consonants.
(Hint: thinking about matching "not"-vowels.)
3. End with `ed`, but not with `eed`.
4. End with `ing` or `ise`.
a. Start with a vowel.
b. That only contain consonants. (Hint: thinking about matching "not"-vowels.)
c. End with `ed`, but not with `eed`.
d. End with `ing` or `ise`.
2. Empirically verify the rule "i before e except after c".
@@ -423,16 +419,16 @@ str_view(x, 'C[LX]+?')
2. Describe in words what these regular expressions match: (read carefully to see if I'm using a regular expression or a string that defines a regular expression.)
1. `^.*$`
2. `"\\{.+\\}"`
3. `\d{4}-\d{2}-\d{2}`
4. `"\\\\{4}"`
a. `^.*$`
b. `"\\{.+\\}"`
c. `\d{4}-\d{2}-\d{2}`
d. `"\\\\{4}"`
3. Create regular expressions to find all words that:
1. Start with three consonants.
2. Have three or more vowels in a row.
3. Have two or more vowel-consonant pairs in a row.
a. Start with three consonants.
b. Have three or more vowels in a row.
c. Have two or more vowel-consonant pairs in a row.
4. Solve the beginner regexp crosswords at <https://regexcrossword.com/challenges/beginner>.
@@ -454,19 +450,17 @@ str_view(fruit, "(..)\\1", match = TRUE)
1. Describe, in words, what these expressions will match:
1. `(.)\1\1`
2. `"(.)(.)\\2\\1"`
3. `(..)\1`
4. `"(.).\\1.\\1"`
5. `"(.)(.)(.).*\\3\\2\\1"`
a. `(.)\1\1`
b. `"(.)(.)\\2\\1"`
c. `(..)\1`
d. `"(.).\\1.\\1"`
e. `"(.)(.)(.).*\\3\\2\\1"`
2. Construct regular expressions to match words that:
1. Start and end with the same character.
2. Contain a repeated pair of letters (e.g. "church" contains "ch" repeated twice.)
3. Contain one letter repeated in at least three places (e.g. "eleven" contains three "e"s.)
a. Start and end with the same character.
b. Contain a repeated pair of letters (e.g. "church" contains "ch" repeated twice.)
c. Contain one letter repeated in at least three places (e.g. "eleven" contains three "e"s.)
## Tools
@@ -666,11 +660,9 @@ The second function will have the suffix `_all`.
1. For each of the following challenges, try solving it by using both a single regular expression, and a combination of multiple `str_detect()` calls.
1. Find all words that start or end with `x`.
2. Find all words that start with a vowel and end with a consonant.
3. Are there any words that contain at least one of each different vowel?
a. Find all words that start or end with `x`.
b. Find all words that start with a vowel and end with a consonant.
c. Are there any words that contain at least one of each different vowel?
2. What word has the highest number of vowels?
What word has the highest proportion of vowels?
@@ -1048,8 +1040,8 @@ The main difference is the prefix: `str_` vs. `stri_`.
1. Find the stringi functions that:
1. Count the number of words.
2. Find duplicated strings.
3. Generate random text.
a. Count the number of words.
b. Find duplicated strings.
c. Generate random text.
2. How do you control the language that `stri_sort()` uses for sorting?