seq() สำหรับลำดับแบบกำหนดเอง

บทนำสู่ seq()

# Basic seq() usage
basic <- seq(1, 10)
cat('seq(1, 10):', basic, '
')

# With step size
by_two <- seq(0, 20, by = 2)
cat('seq(0, 20, by=2):', by_two, '
')

seq(from, to, by) — ก้าวแบบกำหนดเอง

# Decimal step
celsius <- seq(0, 100, by = 12.5)
cat('Every 12.5 degrees:', celsius, '
')

# Step of 0.1
fine_scale <- seq(1.0, 1.5, by = 0.1)
cat('Fine scale:', fine_scale, '
')

# Negative step (descending)
countdown <- seq(10, 0, by = -2)
cat('Countdown by 2:', countdown, '
')

seq(from, to, length.out) — จำนวนค่าคงที่

# 5 evenly spaced points between 0 and 1
unit_interval <- seq(0, 1, length.out = 5)
cat('5 points in [0,1]:', unit_interval, '
')

# 7 breakpoints for a histogram
breakpoints <- seq(0, 100, length.out = 7)
cat('Histogram breaks:', breakpoints, '
')

# Step is automatically calculated
step <- (100 - 0) / (7 - 1)
cat('Step size:', step, '
')

seq(along.with = x) — จับคู่กับเวกเตอร์

rainfall <- c(55.2, 62.1, 48.7, 71.3, 38.9, 90.4, 45.0)

# Generate matching index sequence
idx <- seq(along.with = rainfall)
cat('Indices:', idx, '
')
cat('Rainfall:', rainfall, '
')

# Use to find position of max
cat('Position of max rainfall:', which.max(rainfall), '
')
cat('Max rainfall:', max(rainfall), 'mm
')

seq_len(n) — ปลอดภัยตั้งแต่ 1 ถึง n

# Normal use
cat('seq_len(5):', seq_len(5), '
')

# Edge case: n = 0
cat('1:0       :', 1:0, '
')       # produces 1 0 (WRONG)
cat('seq_len(0):', seq_len(0), '
') # produces integer(0) (CORRECT)

# In practice: safe loop
my_data <- c()  # intentionally empty
for (i in seq_len(length(my_data))) {
  cat('Processing item', i, '
')
}
cat('Loop completed without error
')

ก้าวติดลบด้วย seq()

# Countdown from 100 to 0
countdown_100 <- seq(100, 0, by = -10)
cat('Countdown:', countdown_100, '
')

# Temperature drop simulation
start_temp <- 30.0
end_temp <- 15.0
hourly_temps <- seq(start_temp, end_temp, by = -1.5)
cat('Hourly cooling:', hourly_temps, '
')

ลำดับเลขทศนิยม

# Floating point step: may include or exclude endpoint
seq_by <- seq(0, 1, by = 0.1)
cat('By 0.1 (', length(seq_by), 'values):', seq_by, '
')

# length.out: always exactly n values
seq_lo <- seq(0, 1, length.out = 11)
cat('length.out=11:', seq_lo, '
')

# Check: are they the same?
cat('Identical?', identical(seq_by, seq_lo), '
')

การใช้ seq() สำหรับแกนกราฟ

# Sample a sine wave
x_vals <- seq(0, 2 * pi, length.out = 13)
y_vals <- round(sin(x_vals), 3)
cat('x values (radians):', round(x_vals, 2), '
')
cat('sin(x) values:      ', y_vals, '
')

# Find the approximate peak
cat('Peak near x =', round(x_vals[which.max(y_vals)], 3), '
')

การเปรียบเทียบ seq() กับ :

# These produce the same integer sequence
a <- 1:5
b <- seq(1, 5)
c_seq <- seq(1, 5, by = 1)
d <- seq(1, 5, length.out = 5)

cat('1:5            :', a, '
')
cat('seq(1,5)       :', b, '
')
cat('seq(1,5,by=1)  :', c_seq, '
')
cat('seq(1,5,lo=5)  :', d, '
')
cat('All identical? :', identical(a, d), '
')

ภาคปฏิบัติ: การสร้างจุดเวลา

# Monthly data points (as numeric month indices)
months_idx <- seq(1, 12, by = 1)
month_names <- month.abb  # built-in R constant
cat('Month indices:', months_idx, '
')
cat('Month names  :', month_names, '
')

# Quarterly: every 3 months
quarters <- seq(1, 12, by = 3)
cat('Quarter starts:', quarters, '
')
cat('Quarter names :', month_names[quarters], '
')

สรุปอาร์กิวเมนต์ของ seq()

# Five different forms of seq()
cat('seq(5)               :', seq(5), '
')
cat('seq(2, 10)           :', seq(2, 10), '
')
cat('seq(0, 1, by=0.25)   :', seq(0, 1, by = 0.25), '
')
cat('seq(0, 1, length.out=5):', seq(0, 1, length.out = 5), '
')
cat('seq(along.with=1:4)  :', seq(along.with = 1:4), '
')

ตรวจสอบความเข้าใจอย่างรวดเร็ว

ทบทวน: seq() สำหรับลำดับที่กำหนดเอง

# Final demo: all seq() forms
cat('Even 0-10:    ', seq(0, 10, by = 2), '
')
cat('5 in [0,1]:   ', seq(0, 1, length.out = 5), '
')
cat('Match 3-elem: ', seq(along.with = c('a', 'b', 'c')), '
')
cat('Safe 1:0:     ', seq_len(0), '(empty)
')