Scraping ID attribute using rvest - html

Question

I am trying to check if Polish elections are fair and candidates form opposition did not get abnormal low number of votes in districts with higher amount of invalid votes. To do so I need to scrape results of each district.
Link to official results of elections for my city - in the bottom table, each row is different district and by clicking you get redirected to district. The link is not usual <a ... hef = ...> format, but in the data-id=... is encoded the variable part of the link to districts.
My question is how to extract the data-id= attribute table on a webpage using R?
Sample data - in this example I would like to extract 697773 from row data
<div class="proto" style="">
<div id="DataTables_Table_16_wrapper" class="dataTables_wrapper dt-bootstrap no-footer">
<div class="table-responsive">
<table class="table table-bordered table-striped table-hover dataTable no-footer clickable" id="DataTables_Table_16" role="grid">
<thead><tr role="row"><th class="sorting_asc" tabindex="0" aria-controls="DataTables_Table_16" rowspan="1" colspan="1" aria-sort="ascending" aria-label="Numer: aktywuj, by posortować kolumnę malejąco">Numer</th><th class="sorting" tabindex="0" aria-controls="DataTables_Table_16" rowspan="1" colspan="1" aria-label="Siedziba: aktywuj, by posortować kolumnę rosnąco">Siedziba</th><th class="sorting" tabindex="0" aria-controls="DataTables_Table_16" rowspan="1" colspan="1" aria-label="Granice: aktywuj, by posortować kolumnę rosnąco">Granice</th></tr></thead>
<tbody>
<tr data-id="697773" role="row" class="odd"><td class="sorting_1">1</td><td>Szkoła Podstawowa nr 63</td> <td>Bożego Ciała...</td></tr>
</tbody>
</table>
</div>
</div>
</div>
I have tried using:
library(dplyr)
library(rvest)
read_html("https://wybory.gov.pl/prezydent20200628/pl/wyniki/1/pow/26400") %>%
html_nodes('[class="table-responsive"]') %>%
html_nodes('[class="table table-bordered table-striped table-hover"]') %>%
html_nodes('tr') %>%
html_attrs()
But I get named character(0) as a result

Answer 1

I found not very optimal solution. I bet there is better way!
I have downloaded webpage, saved it as txt file and read from there:
txt_webpage <- readChar(paste0(getwd(), "\\Wyniki pierwszego głosowania _ Wrocław.txt"),
file.info(paste0(getwd(), "\\Wyniki pierwszego głosowania _ Wrocław.txt"))$size)
posiotions <- gregexpr(pattern ='<tr data', txt_webpage)
districts_numbers <- c()
for (i in posiotions[[1]]) {
print (i)
tmp <- substr(txt_webpage, i + 10, i + 22)
tmp <- gsub('\\D+','', tmp)
districts_numbers <- c(districts_numbers, tmp)
}