Coming from R and finding the index rules for pandas dataframes to be not easy to use. I have a dataframe where I want to get the ith row and some columns by their names. I can clearly understand using either iloc or loc as shown below.
df = pd.DataFrame(np.random.randn(8, 4),columns=['A', 'B', 'C', 'D'])df.loc[:,['A', 'B']]df.iloc[0:,0:2]Conceptually what I want is something like:
df.loc[0:,['A', 'B']]Meaning the first row with those columns. Of course that code fails. I can seemingly use:
df.loc[0:0,['A', 'B']]But, this seems strange, though it works. How does one properly index using a combination of row number and column names? In R we would do something like:
df = data.frame(matrix(rnorm(32),8,4))colnames(df) <- c("A", "B", "C", "D") df[1, c('A', 'B')]*** UPDATE *** I was mistaken, the example code above indeed works on this toy dataframe. But, on my real data, I see the following? Both objects are of same type and code is the same, not understanding the error here.
type(poly_set)<class 'pandas.core.frame.DataFrame'>poly_set.loc[:,['P1', 'P2', 'P3']] P1 P2 P329 -2.0897226679999998 -1.237649556 None361 -2.0789117340000001 0.144751427 1.572417454642 -2.0681314259999999 -0.196563749 1.500834574poly_set.loc[0,['P1', 'P2', 'P3']]Traceback (most recent call last): File "C:UsersAppDataLocalProgramsPythonPython38-32libsite-packagespandascoreindexesbase.py", line 2646, in get_loc return self._engine.get_loc(key) File "pandas_libsindex.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc File "pandas_libsindex.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc File "pandas_libshashtable_class_helper.pxi", line 998, in pandas._libs.hashtable.Int64HashTable.get_item File "pandas_libshashtable_class_helper.pxi", line 1005, in pandas._libs.hashtable.Int64HashTable.get_itemKeyError: 0Advertisement
Answer
You are using slicing which means between two given index. If you only want first row data just use:
Try:
df = df.reset_index() df.loc[0,['A', 'B']]