smap - a command line tool for sets and maps

This is a very minimal but powerful tool for performing set/map union, subtraction, and intersection on text files. If you find yourself using commands like sort, uniq, comm, and really contorted sed/awk invocations, this tool will probably help you. It's faster, simpler to use, and doesn't require lexicographic ordering.

Installation:

To install from hackage (without downloading this repo), you will want cabal. Then you can run

cabal install smap

To install from this repo, I recommend getting stack and running

stack install smap

Tutorial:

The setup:

cat > patients << EOF
Bob Smith
Jane Doe
John Smith
Carol Carell
EOF

cat > has_cold << EOF
Jane Doe
John Smith
EOF

cat > has_mumps << EOF
Jane Doe
Carol Carell
EOF

Simple usage (sets)

cat - Set Union (and Deduplication)

Sick patients:

$ smap cat has_cold has_mumps
Jane Doe
John Smith
Carol Carell

You can also use - instead of a filename to represent stdin/stdout. (This works for any command.)

$ cat has_cold | smap cat - has_mumps
Jane Doe
John Smith
Carol Carell

If you don't provide any arguments, cat will assume you mean stdin.

$ cat has_cold has_mumps | smap cat
Jane Doe
John Smith
Carol Carell

By default, output goes to stdout, but you can send it elsewhere with -o. (This also works for any command.)

sub - Set subtraction

Healthy patients:

$ smap sub patients has_cold has_mumps
Bob Smith

int - Set intersection

Patients with both a cold and mumps:

$ smap int has_cold has_mumps
Jane Doe

It's worth noting that both int and sub treat their first argument as a stream, not a set. This means that they won't deduplicate values from their first argument. In practice you will find that this is the most useful arrangement. You can always use smap cat to turn a stream into a set.

To put this all together, let's find patients who only have a cold or mumps, but not both:

$ smap sub <(smap cat has_cold has_mumps) <(smap int has_cold has_mumps)
Carol Carell
John Smith

If you haven't seen the <(command) syntax before, it's a very useful shell tool called process substitution.

Advanced usage (maps)

When using smap with sets, the behavior is pretty straightforward. It gets a bit more complicated when dealing with maps.

There are actually three ways you can pass a file argument to smap.

1. If you just use a regular filepath, like patients.txt or - (for stdin/out), smap will create a map where the keys are equal to the values. This behaves like a set, which is why all the simple usage examples work this way.
2. If you instead use an argument like +file1,file2, smap will use file1 for the keys and file2 for the values.
3. If you instead use an argument like @file, smap will read/write keys/values on alternating lines. This is useful for passing maps between invocations of smap. You can of course use @- to mean "alternating between keys and values on stdin/stdout".

Here are some examples.

Pick one patient from each family:

We can get a list of patient last names using cut -f 2 -d ' ' <patient file>.

$ smap cat +<(cut -f 2 -d ' ' patients),patients
Bob Smith
Jane Doe
Carol Carell

To understand the above:

• <(cut -f 2 -d ' ' patients) gets a list of all the patients' last names and creates a pipe containing this list.
• +<(cut -f 2 -d ' ' patients),patients constructs a stream where the keys are the last names and the values are the whole names.

cat deduplicates by key, so if we see a second (or third, or fourth, etc.) person from a given family we don't print them out.

Patients who have family members with a cold:

$ smap int +<(cut -f 2 -d ' ' patients),patients <(cut -f 2 -d ' ' has_cold)
Bob Smith
Jane Doe
John Smith

To understand the above:

• <(cut -f 2 -d ' ' patients) gets a list of all the patients' last names.
• +<(cut -f 2 -d ' ' patients),patients constructs a stream where the keys are the last names and the values are the whole names.
• <(cut -f 2 -d ' ' has_cold) gets a list of family names of everyone who has a cold.

So int is filtering the first argument (treated as a key,value stream) by the keys present in the second argument.

Passing maps between smap invocations

In earlier examples where we composed invocations of smap, we only passed sets between the various invocations. We can easily pass maps as well, using the @ syntax to read/write keys and values from the same file (on alternating lines). For example, let's say we wanted to find patients whose family members have a cold and mumps. One way we could do it is

$ smap int +<(cut -f 2 -d ' ' patients),patients <(cut -f 2 -d ' ' has_cold) <(cut -f 2 -d ' ' has_mumps)
Jane Doe

Thankfully Jane doesn't have any other family members who are at risk of catching both a cold and mumps. We could also write this as

$ smap int +<(cut -f 2 -d ' ' patients),patients <(cut -f 2 -d ' ' has_cold) -o @- | smap int @- <(cut -f 2 -d ' ' has_mumps)
Jane Doe

What's going on here is that the first command is finding all patients who have a family member with a cold, and outputting to stdout each person's name (the value) as well as their family name (the key). We can see this by running:

$ smap int +<(cut -f 2 -d ' ' patients),patients <(cut -f 2 -d ' ' has_cold) -o @-
Smith
Bob Smith
Doe
Jane Doe
Smith
John Smith

Then, we have a second invocation of smap int which is reading these key/value pairs in from stdin and intersecting them with the set of families where someone has mumps.

Approximate mode

If you're processing lots of lines and running up against memory limits, you can use the --approximate or -a option to keep track of a 64-bit hash of each line instead of the entire line. You can also use --approx-with-key or -k if you want to specify the SipHash key.

Illustrative example:

$ smap sub -a +<(cut -f 2 -d ' ' patients),patients -o @-
5e1334422d6eedac
Bob Smith
c62edd9db8aac96c
Jane Doe
5e1334422d6eedac
John Smith
79db904924f32d34
Carol Carell

Notice that the Smiths both have a key of 5e13...

Performance

It's pretty fast. On my laptop, I can churn through 1.something million lines per second for short lines and a few hundred megabytes per second on long lines. I'll probably run out of RAM before I run out of time. Of course, faster is better, so please feel free to open an issue/PR with suggestions.