In rdpla: Client for the Digital Public Library of America ('DPLA')

knitr::opts_chunk$set(
    comment = "#>",
    collapse = TRUE,
    warning = FALSE,
    message = FALSE,
    fig.path = "figure/"
)

rdpla use case: vizualize churches across DPLA holdings

To aid users in what can be done with rdpla, the following is one example.

Use case:

Search for all photos of churches and make a visualization through time and facet by other factors

Get item data

library("rdpla")
library("data.table")
library("lubridate")

To get all data for subject:churches and of type=image we'd need to do about 100 requests of size 500 records, but we'll just do one that so the example runs quickly.

res <- dpla_items(subject = "churches", type = "image", page_size = 500)
df <- res$data

Parse data

dates <- unlist(df$date, use.names = FALSE)
# remove 2nd part of a duration separted by " - ", just use first date
dates <- gsub("\\s-\\s.+", "", dates)
# remove 2nd part of a duration separted by "/", just use first date
dates <- gsub("/.+", "", dates)
# remove 2nd part of a duration separted by "-", just use first date
dates <- gsub("-[0-9]{4}", "", dates)
# remove any text, can't parse it
dates <- gsub("[[:alpha:]]+", "", dates)
# trim leading and trailing white space
dates <- gsub("^\\s+|\\s+$", "", dates)
# parse dates
df$date_corr <- parse_date_time(dates, c("Y", "ymd", "ym", "%Y-%m-%d%H:%M:%S%z"))

Make year column

df$year <- year(df$date_corr)

Summarize by year

df_dt <- as.data.table(df)
df_dt <- df_dt[order(year)]
df_sum <- df_dt[, list(count = length(id)), by = year]
df_sum <- as.data.frame(na.omit(df_sum))

Vizualize

library("ggplot2")

ggplot(df_sum, aes(x = year, y = count)) + 
  geom_bar(stat = "identity") + 
  theme_gray(base_size = 18)

Zooming in on the majority of the data

ggplot(subset(df_sum, year > 1800), aes(x = year, y = count)) + 
  geom_bar(stat = "identity") + 
  theme_gray(base_size = 18)

Looks like there's a big spike in r df_sum[which.max(df_sum$count), "year"]

Let's have a look at a few of the titles

sort(unique(subset(df, year == 1930)$title))[1:10]

rdpla documentation built on May 2, 2019, 2:31 p.m.