Write Pandas DataFrame to newline-delimited JSON

If you're trying to write a DF using iterrows - I suspect you should be looking at:

df.to_json(orient='records') # List of lists of values
# [[1, 2], [3,4]]

Or:

df.to_json(orient='records') # List of dicts with col->val
# [{'A': 1, 'B': 2}, {'A': 3, 'B': 4}]

Or writing a dict of {index:col value}:

df.A.to_json()
# {0: 1, 1: 3}

To create newline-delimited json from a dataframe df, run the following

df.to_json("path/to/filename.json",
           orient="records",
           lines=True)

Pay close attention to those optional keyword args! The lines option was added in pandas 0.19.0.

You can pass a buffer in to df.to_json():

In [1]: import pandas as pd

In [2]: df = pd.DataFrame({"a":[1,3,5], "b":[1.1,1.2,1.2]})

In [3]: df
Out[3]: 
   a    b
0  1  1.1
1  3  1.2
2  5  1.2

In [4]: f = open("temp.txt", "w")

In [5]: for row in df.iterrows():
    row[1].to_json(f)
    f.write("\n")
   ...:     

In [6]: f.close()

In [7]: open("temp.txt").read()
Out[7]: '{"a":1.0,"b":1.1}\n{"a":3.0,"b":1.2}\n{"a":5.0,"b":1.2}\n'