### pdbensure - ensure certain columns are present in the data

`pdbensure` either simply drops rows without content in a list of
columns, or optionally fills in the values with a default instead.

#### Example input (*myfile.fsdb*):

```
#fsdb -F s col1:l two:a andthree:d
1	key1	42.0
2	key2	
3	    90.2
```

#### Example command usage

```
$ pdbensure -c andthree -e myfile.fsdb
```

#### Example output

```
#fsdb -F t col1:l two:a andthree:d
1		42.0
# dbensure dropping row:[2, 'key2', None]
3		90.2
```

#### Example command usage -- adding a second column

```
$ pdbensure -c andthree two -e myfile.fsdb
```

#### Example output

```
#fsdb -F t col1:l two:a andthree:d
1		42.0
# dbensure dropping row:[2, 'key2', None]
# dbensure dropping row:[3, None, 90.2]
```

#### Example command usage -- with replacement

```
$ pdbensure -c two -v replace -- myfile.fsdb
```

#### Example output

```
#fsdb -F t col1:l two:a andthree:d
1	key1	42.0
2	key2	
3	replace	90.2
```