Crash when provided train data and test data do not have same number of columns

[comunidadio]

flight_delays dataset as per https://www.kaggle.com/c/flight-delays-spring-2018

On tangram 0.7:

 $ tangram train --file-train flight_delays_train.csv --file-test flight_delays_test.csv --target dep_delayed_15min
✅ Inferring train table columns. 0s 43ms
✅ Loading train table. 0s 40ms
✅ Loading test table. 0s 45ms
✅ Shuffling. 0s 9ms
✅ Computing train stats. 0s 121ms
✅ Computing test stats. 0s 112ms
✅ Finalizing stats. 0s 1ms
error: panicked at 'removal index (is 8) should be < len (is 8)', library/alloc/src/vec/mod.rs:1385:13
   0: backtrace::capture::Backtrace::new
   1: tangram::train::train::{{closure}}
   2: std::panicking::rust_panic_with_hook
   3: std::panicking::begin_panic_handler::{{closure}}
   4: std::sys_common::backtrace::__rust_end_short_backtrace
   5: _rust_begin_unwind
   6: core::panicking::panic_fmt
   7: alloc::vec::Vec<T,A>::remove::assert_failed
   8: tangram_core::train::Trainer::prepare
   9: tangram::main
  10: std::sys_common::backtrace::__rust_begin_short_backtrace
  11: _main

Noticed slightly different stacktrace with tangram latest (main branch):

 $ tangram-tip train --file-train flight_delays_train.csv --file-test flight_delays_test.csv --target dep_delayed_15min
✅ Inferring train table columns. 0s 48ms
✅ Loading train table. 0s 41ms
✅ Loading test table. 0s 44ms
✅ Shuffling. 0s 9ms
✅ Computing train stats. 0s 115ms
✅ Computing test stats. 0s 119ms
✅ Finalizing stats. 0s 1ms
error: panicked at 'removal index (is 8) should be < len (is 8)', crates/core/train.rs:176:58
   0: backtrace::capture::Backtrace::new
   1: tangram::train::train::{{closure}}
   2: std::panicking::rust_panic_with_hook
   3: std::panicking::begin_panic_handler::{{closure}}
   4: std::sys_common::backtrace::__rust_end_short_backtrace
   5: _rust_begin_unwind
   6: core::panicking::panic_fmt
   7: alloc::vec::Vec<T,A>::remove::assert_failed
   8: tangram_core::train::Trainer::prepare
   9: tangram::main
  10: std::sys_common::backtrace::__rust_begin_short_backtrace
  11: _main

[comunidadio]

Oops... didn't realize Kaggle's "test data" is without label column as it's for blind testing. I guess the issue here is more about showing an error message rather a crash stacktrace when columns differ between tangram's train and test sets?

[nitsky]

@comunidadio thanks for opening this issue. We should show a good error message in this case. We will have a fix pushed shortly.

[deciduously]

Good catch @comunidadio - this commit will now quit gracefully in this case.