Hacker News Reader

Comment by chaps | Hacker News Reader

Hah, I'd love to work with the datasets you work with if it takes five minutes to do this. Or maybe you're just suggesting it takes five minutes to write out "TEXT" for each column type?

The data I work with is messy, from hand written notes, multiple sources, millions of rows, etc etc. A single point that's written as "one" instead of 1 makes your whole idea fall on its face.

View on HN

For pile-of-strings data, there are still things you can do. E.g. in Pandas, if there are a small number of different values, switch to categoricals (https://pythonspeed.com/articles/pandas-load-less-data/ item 3). And there's a new column type for strings that uses less memory (https://pythonspeed.com/articles/pandas-string-dtype-memory/).

Tried that in the past, but it's really slow. Pandas is effectively removed from my workflows because of issues like this.

But, I have workarounds for these issues by loading everything into postgres under TEXT columns in a "raw" schema, then do some typecast tests in a descending list of types to get the smallest possible type to transfer to a new table in a "prod" schema. It's read-only data, so it's not a big deal to run it once, and builds out a chain of changes from csv -> sql.

Something like this could be done with pickling to avoid having to re-type every time I run the code (and I've done that for some past projects, but it's... ehhh).

Perhaps do the data-cleaning step before loading into a data frame? (Dataframes are, after all, for canonicalized+normalized data, just like RDBMS tables are.)

No way. The initial loading into a dataframe takes way too long to make it useful for exploratory work. Load it into a database is done once and forget it. In the long run, the time wasted loading things into dataframes over and over and over again just isn't worth it. Keep in mind that we're talking about large datasets that may or may not fit into memory.

"Oops, messed up my import slightly. Gotta run it again and wait ages.... again"

"Oops, loaded the dataframe twice on accident and had OOM. Gotta restart from the beginning... again"

"Oops, forgot to .head(5) my dataframe and jupyter's crashed... again..."

Doing everything in SQL solves so many problems. And OOM is practically a non-issue.

For exploratory work, perhaps you should random sample some of the dataset (say 1k) and see the effect on them? After getting good result, you then switch to dealing with the whole dataset.

No need in my workflows since unix tools solve that exploratory starting point. Just about everything else is SQL.

Is enough data generated from handwritten notes that the memory cost is a serious problem? I was under the impression that hundreds of books worth of text fit in a gigabyte.

It can be! I have a 50m row dataset of handwritten notes that's large, but when loaded into pandas, it blooms wayyyy larger than its underlying files.

Reply on news.ycombinator.com