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Needs an explanation for Indexer #39
Description
A number of methods (at, select_columns) refer to the indexer without ever explaining what it is and the concept behind it. I've got a vague idea from reading around Numpy/Pandas, but I can't guess at why my code doesn't always do what I expect. Probably hidden away by the _internal data structure. It'll help people coming at this for the first time.
It could explain why these two methods stringify the same, but they don't coerce the same
$h1 = double $df->at(6)
[ 1,344.5 1,309.3 1,295.5 1,292.4 1,258]
$h2 = double $df->columns( 'Height' )
[0 1 2 3 4 5]
for inspiration - https://pandas.pydata.org/docs/user_guide/indexing.html
Activity
mohawk2 commentedon Sep 5, 2026
Feel like investigating by reading the code, and then capturing findings in another doc update?
duffee commentedon Sep 6, 2026
Unfortunately, I'll be starting a new job in a few weeks, so that investigation will get pushed onto the back burner (I've made a note for when I get around to writing up a blog post on Data::Frame). This drive-by was a side effect of trying to make an HTML table to Data::Frame converter, like Pandas has.
mohawk2 commentedon Sep 6, 2026
Fair enough. Congrats on the new job, and hope you'll be at LPW.
Can you point at some docs for the HTML scraper that Pandas has?
duffee commentedon Sep 6, 2026
I'm aiming for LPW, but haven't thought about what I should prepare for it.
Using any library to download the html or given one saved on the filesystem, it uses pandas.read_html to extract the data. The note in McKinney's Python for Data Analysis says "by default it searches for and attempts to parse all tabular data contained within
<table>tags. The result is a list of DataFrame objects" like soA small headache is that my current script slurps everything into a Data::Frame as a PDL::SV, even the numeric data, meaning that you can't get a nice
summaryof the data as it thinks they're all strings.Another example that fetches a page https://stackoverflow.com/questions/39120853/converting-an-html-table-in-pandas-dataframe
mohawk2 commentedon Sep 6, 2026
I'd hope it's fine to just turn up without preparing. I wasn't planning to prepare anything.
Cool! I'd encourage you to put what you've got somewhere (maybe on this issue?) to inspire others.