Some notable other APIs useful for digital marketing are described below:

Search Console

Get your SEO keywords back after (not provided) via Google’s Search Console.

## This installs searchConsoleR if you haven't got it already
if(!require(searchConsoleR)) install.packages("searchConsoleR")
library(searchConsoleR)

## authentication similar to googleAnalyticsR
scr_auth()

seo_data <- search_analytics("your-website.com", dimensions = c("date","query"))

BigQuery

Useful if you have Big Query exports from Google Analytics 360. See BigQuery section of googleAnalyticsR.

## This installs bigQueryR if you haven't got it already
if(!require(bigQueryR)) install.packages("bigQueryR")

library(googleAnalyticsR)

## authentication similar to googleAnalyticsR
bqr_auth()

## this function turns GA dimensions/metrics into BigQuery SQL

bq <- google_analytics_bq("project-id", "dataset-id-ga-viewid", 
                           start = "2016-01-01", end = "2016-02-01", 
                           metrics = "users", 
                           dimensions = c("source","medium"))
head(bq)
             source   medium  users
1   mavas|blahbs.ru  display  47837
2          examp.ae referral   6090
3   lm.facebook.com referral    335
4       ghtie_yahoo  display 133900
5      fjsfs_inmobi  display  19887
6 tripadvisor.co.dk referral    307

For more general BigQuery extracts, it may be better to use the more developed bigrquery() instead.