QST: No common columns to perform merge on
```
frequency = 'monthly'
start = '1969-12-31'
end = '2020-12-31'
data = quandl.get(["ISM/MAN_PMI"], trim_start=start, trim_end=end)
data.head()
```
ISM/MAN_PMI - PMI Date
1970-01-01 48.7 1970-02-01 47.4 1970-03-01 46.9 1970-04-01 45.0 1970-05-01 47.2

```
df_log = numpy.log(df / df.shift(1))
df_log.head()
```
Adjusted Close Date
1969-12-31 NaN 1970-01-30 -0.079554 1970-02-27 0.051352 1970-03-31 0.001451 1970-04-30 -0.094842

`pd.merge(df, data)`
Error: MergeError: No common columns to perform merge on. Merge options: left_on=None, right_on=None, left_index=False, right_index=False


How chan I merge the two tables and harmonize them to:

1969-12 
1970-1
 1970-2 
1970-3 
..
 ..