nchar and substring in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the number of characters in the string.

R Programming

length <- [1]("Hello World")

Drag options to blanks, or click blank then click option'

Asubstring

Bnchar

Clength

Dstr_length

Attempts:

3 left

💡 Hint

Common Mistakes

Using substring instead of nchar.

Using length which counts elements in a vector, not characters.

The nchar() function returns the number of characters in a string in R.

2fill in blank

medium

Complete the code to extract the first 5 characters from the string.

R Programming

part <- [1]("Programming", 1, 5)

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Asubstring

Bstr_sub

Csubstr

Dnchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using nchar which counts characters, not extracts.

Using str_sub which is from a different package.

The substring() function extracts a substring from a string given start and end positions.

3fill in blank

hard

Fix the error in the code to correctly extract characters 3 to 7 from the string.

R Programming

result <- substring("DataScience", [1], 7)

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A1

B7

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 7 as start position which extracts only one character.

Using 0 which is invalid in R string indexing.

The start position should be 3 to extract characters from position 3 to 7.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

R Programming

lengths <- list([1] = nchar(word) for word in words if nchar(word) [2] 3)

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Aword

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which selects words exactly 3 characters long.

Using < which selects shorter words.

We use word as the key and check if word length is greater than 3 with >.

5fill in blank

hard

Fill all three blanks to create a named vector of substring results for words longer than 4 characters.

R Programming

result <- c([1] = substring(word, 1, 3) for word in words if nchar(word) [2] 4 and word [3] "Data")

Drag options to blanks, or click blank then click option'

Aword

B>

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of != which would include only "Data".

Using < instead of > which selects shorter words.

We use word as the name, select words with length greater than 4, and exclude the word "Data" using !=.

Practice

1. What does the nchar function do in R?

easy

A. Returns the number of characters in a string

B. Extracts a substring from a string

C. Converts a string to uppercase

D. Counts the number of words in a string

Solution

1. Step 1: Understand the purpose of nchar

   The nchar function counts how many characters are in a string, including spaces and punctuation.

2. Step 2: Compare with other options

   Other options describe different functions: substring extracts parts, toupper converts case, and word count is not done by nchar.

3. Final Answer:

   Returns the number of characters in a string -> Option A

4. Quick Check:

   nchar("hello") = 5 [OK]

Hint: Remember: nchar counts characters, substring extracts parts [OK]

Common Mistakes:

• Confusing nchar with substring
• Thinking nchar counts words
• Assuming nchar changes the string

2. Which of the following is the correct way to extract the substring "cat" from the string "concatenate" in R?

easy

A. substring("concatenate", 3, 5)

B. substring("concatenate", 4, 6)

C. substring("concatenate", 5, 7)

D. substring("concatenate", 2, 4)

Solution

1. Step 1: Identify the position of "cat" in "concatenate"

   "concatenate" is c(1)o(2)n(3)c(4)a(5)t(6)e(7)n(8)a(9)t(10)e(11). The substring "cat" starts at position 4 and ends at 6.

2. Step 2: Use substring with correct start and end

   Using substring("concatenate", 4, 6) extracts characters 4 to 6, which is "cat".

3. Final Answer:

   substring("concatenate", 4, 6) -> Option B

4. Quick Check:

   substring("concatenate", 4, 6) = "cat" [OK]

Hint: Count characters starting at 1 to find substring positions [OK]

Common Mistakes:

• Starting count at 0 instead of 1
• Mixing up start and end positions
• Using incorrect substring indices

3. What will be the output of this R code?

text <- "Programming"
len <- nchar(text)
sub <- substring(text, 4, 7)
print(len)
print(sub)

medium

A. 11 and "gram"

B. 11 and "gramm"

C. 10 and "gram"

D. 10 and "gramm"

Solution

1. Step 1: Calculate length of "Programming" using nchar

   "Programming" has 11 characters: P(1) r(2) o(3) g(4) r(5) a(6) m(7) m(8) i(9) n(10) g(11). So, len = 11.

2. Step 2: Extract substring from position 4 to 7

   Characters 4 to 7 are g(4) r(5) a(6) m(7), so substring is "gram".

3. Final Answer:

   11 and "gram" -> Option A

4. Quick Check:

   nchar("Programming") = 11, substring(4,7) = "gram" [OK]

Hint: Count characters carefully; substring includes both start and end [OK]

Common Mistakes:

• Counting length as 10 instead of 11
• Extracting one extra character in substring
• Confusing substring end position as exclusive

4. The following code is intended to extract "data" from the string "database" but it gives wrong output. What is the error?

text <- "database"
result <- substring(text, 1, 3)
print(result)

medium

A. The string variable is misspelled

B. substring function syntax is wrong

C. nchar should be used instead of substring

D. Start and end positions are incorrect; should be 1 to 4

Solution

1. Step 1: Check the substring positions used

   substring(text, 1, 3) extracts characters 1 to 3: "dat" from "database".

2. Step 2: Identify correct positions for "data"

   "data" is characters 1 to 4, so end position should be 4, not 3.

3. Final Answer:

   Start and end positions are incorrect; should be 1 to 4 -> Option D

4. Quick Check:

   substring("database", 1, 4) = "data" [OK]

Hint: Remember substring end position is inclusive [OK]

Common Mistakes:

• Using end position one less than needed
• Confusing substring with nchar usage
• Assuming substring excludes end position

5. You have a vector of strings: words <- c("apple", "banana", "cherry"). Write R code using substring and nchar to create a new vector containing the last 3 characters of each word. Which code snippet does this correctly?

hard

A. substring(words, nchar(words), nchar(words)+2)

B. substring(words, 1, 3)

C. substring(words, nchar(words)-2, nchar(words))

D. substring(words, nchar(words)-3, nchar(words)-1)

Solution

1. Step 1: Understand how to get last 3 characters

   For each word, last 3 characters start at position (length - 2) and end at length. Use nchar(words) to get length.

2. Step 2: Use substring with vectorized start and end

   substring(words, nchar(words)-2, nchar(words)) extracts last 3 characters for each word correctly.

3. Step 3: Check other options

   substring(words, 1, 3) extracts first 3 characters, C uses invalid end position, D extracts wrong positions.

4. Final Answer:

   substring(words, nchar(words)-2, nchar(words)) -> Option C

5. Quick Check:

   Last 3 chars of "banana" = "ana" [OK]

Hint: Use nchar(word)-2 as start for last 3 chars [OK]

Common Mistakes:

• Using fixed start positions instead of dynamic
• Off-by-one errors in start or end positions
• Assuming substring end is exclusive