Looks like a data race, after testing it with the -race detector.

```
==================
WARNING: DATA RACE
Read by goroutine 4:
  github.com/sjwhitworth/golearn/meta.func·001()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:78 +0x59

Previous write by goroutine 3:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:76 +0x198
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:39 +0x32d
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:23 +0x36b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f

Goroutine 4 (running) created at:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:81 +0x270
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:39 +0x32d
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:23 +0x36b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f

Goroutine 3 (running) created at:
  testing.RunTests()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:471 +0xb3c
  testing.Main()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:403 +0xa2
  main.main()
      github.com/sjwhitworth/golearn/ensemble/_test/_testmain.go:47 +0xdc
==================
==================
WARNING: DATA RACE
Write by goroutine 4:
  runtime.mapassign1()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/runtime/hashmap.c:1134 +0x0
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).generateTrainingAttrs()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:50 +0x44b
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).generateTrainingInstances()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:61 +0x7c
  github.com/sjwhitworth/golearn/meta.func·001()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:78 +0x80

Previous write by goroutine 5:
  runtime.mapassign1()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/runtime/hashmap.c:1134 +0x0
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).generateTrainingAttrs()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:50 +0x44b
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).generateTrainingInstances()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:61 +0x7c
  github.com/sjwhitworth/golearn/meta.func·001()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:78 +0x80

Goroutine 4 (running) created at:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:81 +0x270
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:39 +0x32d
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:23 +0x36b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f

Goroutine 5 (running) created at:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:81 +0x270
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Fit()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:39 +0x32d
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:23 +0x36b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f
==================
==================
WARNING: DATA RACE
Read by goroutine 14:
  github.com/sjwhitworth/golearn/meta.func·002()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:100 +0x59

Previous write by goroutine 3:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Predict()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:98 +0x169
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Predict()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:44 +0x55
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:24 +0x39b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f

Goroutine 14 (running) created at:
  github.com/sjwhitworth/golearn/meta.(*BaggedModel).Predict()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/meta/bagging.go:103 +0x25c
  github.com/sjwhitworth/golearn/ensemble.(*RandomForest).Predict()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest.go:44 +0x55
  github.com/sjwhitworth/golearn/ensemble.TestRandomForest1()
      /Users/stephenwhitworth/src/github.com/sjwhitworth/golearn/ensemble/randomforest_test.go:24 +0x39b
  testing.tRunner()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:391 +0x10f

Goroutine 3 (running) created at:
  testing.RunTests()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:471 +0xb3c
  testing.Main()
      /opt/boxen/homebrew/Cellar/go/1.2.1/libexec/src/pkg/testing/testing.go:403 +0xa2
  main.main()
      github.com/sjwhitworth/golearn/ensemble/_test/_testmain.go:47 +0xdc
```

```
go version go1.2.1 darwin/amd6
```

On Mac OSX 10.9.2