14 图书逾期费

图书馆借的书产生了逾期费

Published

January 21, 2026

1. 图书馆借的书逾期了将近半年

# Load packages
ggplot2 |> library() # for plotting
magick |> library() # for reading image
grid |> library() # for changing image to graphic object

# Read the image of book return receipt
book_return_receipt <- "images/return-certificate.jpg" |> 
    magick::image_read()

book_return_receipt_grob <- book_return_receipt |>
    grid::rasterGrob() # change to graphic object

book_return_receipt_dimention <- book_return_receipt |> 
    magick::image_info() # get the width, height, and beyond
book_return_receipt_dimention |> print()

# Plot and mask
df <- data.frame(
    x = seq(1, 827, by = 1), # the width of receipt is 827
    y = seq(1, 827, by = 1) # the height of receipt is 479
)

book_return_receipt_plot <- df |> 
    ggplot(aes(x = x, y = y)) +
    annotation_custom(
        book_return_receipt_grob,
        xmin = 1,
        xmax = 827,
        ymin = 1,
        ymax = 479
    ) +
    geom_point(alpha = 0) +
    annotate("rect", xmin = 45, xmax = 160, ymin = 400, ymax = 417, alpha = 1) + # mask library name
    annotate("rect", xmin = 465, xmax = 575, ymin = 402, ymax = 419, alpha = 1) + # mask library name
    annotate("segment", x = 45, xend = 245, y = 373, yend = 373, colour  = "red") + # mark return date
    annotate("segment", x = 465, xend = 660, y = 373, yend = 373, colour = "red") + # mark return date
    annotate("segment", x = 230, xend = 330, y = 249, yend = 249, colour = "blue") + # mark due date
    annotate("segment", x = 45, xend = 145, y = 226, yend = 226, colour = "blue") +
    annotate("segment", x = 650, xend = 750, y= 255, yend = 255, colour = "blue") + # mark due date
    annotate("segment", x = 468, xend = 568, y = 230, yend = 230, colour = "blue") +
    annotate("rect", xmin = 170, xmax = 345, ymin = 80, ymax = 105, alpha = .2, fill = "yellow") + # mark overdue fee/day
    annotate("rect", xmin = 45, xmax = 68, ymin = 55, ymax = 80, alpha = .2, fill = "yellow") + 
    annotate("rect", xmin = 590, xmax = 768, ymin = 84, ymax = 107, alpha = .2, fill = "yellow") + # mark overdue fee/day
    annotate("rect", xmin = 467, xmax = 488, ymin = 61, ymax = 82, alpha = .2, fill = "yellow") + 
    scale_x_continuous(limits = c(1, 827)) +
    scale_y_continuous(limits = c(1, 479)) +
    theme_void()

"images/return-certificate_mask.png" |> ggsave(
    book_return_receipt_plot, 
    width = 8.27, 
    height = 4.79, 
    units = "cm")

能够看出来：

应还日期为：2025-07-05。
还书日期为：2026-01-13。
逾期费为：0.2元/天。

2. 逾期费计算

due_date <- "2025-07-05" |> 
    as.Date()

return_date <- "2026-01-13" |> 
    as.Date()

# Calculate overdue time
overdue_time <- difftime(return_date, due_date, units = "days")
paste0("每本书的逾期天数为：", overdue_time, " 天。") |> print()

[1] "每本书的逾期天数为：192 天。"

# Calculate overdue fee
overdue_fee_per_day <- 0.2
overdue_fee <- overdue_time * overdue_fee_per_day * 2 # two books
paste0("两本书的逾期总费用为：", overdue_fee, " 元。") |> print()

[1] "两本书的逾期总费用为：76.8 元。"

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