Update your results using the recorded workflow

Here, we will quickly see one of the advantages of using the renku command line tool.

Check the file data/output/flights-count.txt; in it, you should see that there were 23078 flights to Austin, TX in Jan 2019.

This does not seem quite right. Austin, TX is not a very large airport, but that number would mean that it had a flight landing on average every two minutes, around the clock, during the entire month of January 2019.

Go back and take a look at the filtering script: it contains an error! In the code block

# Select only flights to Austin (AUS)
df = df[df['DEST'] == 'DFW']
# Filter to flights to Austin, TX
df = full_df[full_df.DEST .== "DFW", :]
# Select only flights to Austin (AUS)
data %>% filter(DEST == "DFW")

we want to select flights to Austin-Bergstrom (AUS), but mistakenly select flights to a different airport, DFW. This would explain the discrepancy we found. Dallas/Fort Worth is a much larger airport!

Let us fix this. Change DFW to AUS and save the file. Now when you execute git status you should see something like the following:

$ git status

On branch master
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   src/filter_flights.py

no changes added to commit (use "git add" and/or "git commit -a")

Since we have made a change to our code, we need to commit the updated file to the repository.

$ renku save -m 'fix filter error'


Now that we have made this change, how would you update everything without Renku? Without Renku, you would need to think back and remember what files would be affected by this change and what commands were run to initially create them. To effect an update, you would manually carry out those steps again, while being careful to do so in the correct order.

So without Renku, updating a project in response to a change can be tedious and error-prone. But with Renku, it is very easy. We can just ask the system what changed and what needs to be updated. The outputs are analogous for all programming languages.

$ renku status
Outdated outputs(2):
(use `renku workflow visualize [<file>...]` to see the full lineage)
(use `renku update --all` to generate the file from its latest inputs)

    data/output/flights-count.txt: src/filter_flights.py
    data/output/flights-filtered.csv: src/filter_flights.py

Modified inputs(1):


Renku is telling us that src/filter_flights.py was changed and data/output/flights-filtered.csv, data/output/flights-count.txt all need to be updated as a result. We do not need to remember how to update them: Renku already knows this. We can just ask it to make the update by running renku update --all or renku update data/output/flights-filtered.csv data/output/flights-count.txt.

$ renku update --all

[workflow ] start
There were 4951 flights to Austin, TX in Jan 2019.

[job step_1] completed success
[step step_1] completed success
[workflow ] completed success
Moving outputs  [                                    ]  2/2

Wasn’t that easy!?

Now, if you look at data/output/flights-count.txt, you should see that there were 4951 flights to Austin, TX in Jan 2019, which sounds plausible.

Before calling it a day, we should not forget to push our work:

$ renku save