I am trying to create an index in RethinkDB.
The documents look like this:

```
{ "pinyin" : "a1 ai3"}

```

To make searching easier, I would like to preprocess the index entries and remove spaces and numbers, the entry thus should simply be "aai" in this case. What I tried are various variants of the following:

```
r.index_create('pinyin', lambda doc: doc['pinyin'].replace("1", "")).run()

```

This is a most simple case to build from, but even here I get an error 

```
Expected 2 arguments but found 3 in:
r.table('collection').index_create('pinyin', lambda var_7:   var_7['pinyin'].replace('1', ''))

```

It's obvious that I do not understand what's going on. Can anybody help? I gather that the lambda expression has to follow python syntax, but since it will be used on the server has to be JavaScript??