# Data-cleaning examples

Here are some ways to use the type-checking options as described in the [Type-checking page](reference-dsl-variables.md#type-checking).  Suppose you have the following data file, with inconsistent typing for boolean. (Also imagine that, for the sake of discussion, we have a million-line file rather than a four-line file, so we can't see it all at once and some automation is called for.)

GENMD-RUN-COMMAND
cat data/het-bool.csv
GENMD-EOF

One option is to coerce everything to boolean, or integer:

GENMD-RUN-COMMAND
mlr --icsv --opprint put '$reachable = boolean($reachable)' data/het-bool.csv
GENMD-EOF

GENMD-RUN-COMMAND
mlr --icsv --opprint put '$reachable = int(boolean($reachable))' data/het-bool.csv
GENMD-EOF

A second option is to flag badly formatted data within the output stream:

GENMD-RUN-COMMAND
mlr --icsv --opprint put '$format_ok = is_string($reachable)' data/het-bool.csv
GENMD-EOF

Or perhaps to flag badly formatted data outside the output stream:

GENMD-RUN-COMMAND
mlr --icsv --opprint put '
  if (!is_string($reachable)) {eprint "Malformed at NR=".NR}
' data/het-bool.csv
GENMD-EOF

A third way is to abort the process on first instance of bad data:

GENMD-RUN-COMMAND-STDERR-ONLY
mlr --csv put '$reachable = asserting_string($reachable)' data/het-bool.csv
GENMD-EOF
