Pandas: How to index rows?

Question

I have a dataset like this:

stock_symbol    stock_date      stock_price_open     stock_price_high   
QRR             8/2/10  2.37    2.42                 2.29
QTM             5/2/10  2.38    2.5                  2.34
QXM             4/2/10  2.57    2.64                 2.39

I read a NYSE dataset: df = pandas.read_csv('NYSE.csv', index_col = 0, parse_dates=True)

When I ran: df[['QRR','QTM','QXM']]

I got this error: KeyError: "['QRR' 'QTM' 'QXM'] not in index"

'QRR', 'QTM', 'QXM' are values of stock_symbol column. Could anyone please show me how to index them?

Andy Hayden · Accepted Answer · 2015-02-03 07:21:30Z

2

You have to use loc:

In [11]: df.loc[['QRR','QTM','QXM']]
Out[11]:
                stock_date  stock_price_open  stock_price_high
stock_symbol
QRR           8/2/10  2.37              2.42              2.29
QTM           5/2/10  2.38              2.50              2.34
QXM           4/2/10  2.57              2.64              2.39

Without loc, df[['QRR','QTM','QXM']], pandas is trying to select those columns (which don't exist, hence the "not in index" message):

In [21]: df[["stock_price_open", "stock_price_high"]]
Out[21]:
              stock_price_open  stock_price_high
stock_symbol
QRR                       2.42              2.29
QTM                       2.50              2.34
QXM                       2.64              2.39

check out the selecting data section of the docs.

edited Feb 3, 2015 at 7:21

answered Feb 3, 2015 at 7:06

Andy Hayden

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2 Comments

Kiem Nguyen Over a year ago

Thanks Andy, I thought when I create a DataFrame from the .csv dataset with this code: df = pandas.read_csv('NYSE.csv', index_col = 0, parse_dates=True) The index_col = 0 would set index for the first column (stock_symbol)

Andy Hayden Over a year ago

@KiemNguyen ah, yes it does precisely that! ok you just need to use loc :) updated the answer

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