I have a feeling there is a simple way to do this... I have a dataframe as follows:

```
df1 =
Index A B C
0 5 7 11
1 10 7 11
```

I am trying to figure out how to:

```
df1['Index'==1][<10].count()
```

Ie, for index = 1, return the number of values that are <10. (so should return 1)

Thanks!

You can do the selection using `DF.query()`

as follows: (assuming you want to query the index axis which may be duplicated)

```
df1.query("Index == 1").lt(10).sum(1) # assuming the index name as "Index"
Out[56]:
Index
1 1
dtype: int64
```

It's `.loc`

equivalent syntax:

```
df1.loc[df1.index==1].lt(10).sum(1)
Out[58]:
Index
1 1
dtype: int64
```