Constructing pandas DataFrame from values in variables gives ValueError If using all scalar values you must pass an index

Question

This may be a simple question  but I can not figure out how to do this  Lets say that I have two variables as follows   a   2 b   3   I want to construct a DataFrame from this   df2   pd DataFrame   A  a  B  b     This generates an error        ValueError  If using all scalar values  you must pass an index   I tried this also   df2    pd DataFrame   a  a  b  b    reset index     This gives the same error message

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You may try wrapping your dictionary in to list  my dict     A  1  B  2   pd DataFrame  my dict       A  B 0  1  2

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Convert Dictionary to Data Frame  col dict df   pd Series col dict  to frame  new col   reset index     Give new name to  Column  col dict df columns     col1    col2

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If you intend to convert a dictionary of scalars  you have to include an index   import pandas as pd  alphabets     A    a    B    b   index    0  alphabets df   pd DataFrame alphabets  index index  print alphabets df    Although index is not required for a dictionary of lists  the same idea can be expanded to a dictionary of lists   planets     planet     earth    mars    jupiter     length of day     1    1 03    0 414    index    0  1  2  planets df   pd DataFrame planets  index index  print planets df    Of course  for the dictionary of lists  you can build the dataframe without an index   planets df   pd DataFrame planets  print planets df

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I had the same problem with numpy arrays and the solution is to flatten them   data          b   array1 flatten         a   array2 flatten       df   pd DataFrame data

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You can also use pd DataFrame from records which is more convenient when you already have the dictionary in hand   df   pd DataFrame from records     A  a  B  b       You can also set index  if you want  by   df   pd DataFrame from records     A  a  B  b     index  A

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the input does not have to be a list of records - it can be a single dictionary as well   pd DataFrame from records   a  1  b  2   index  0      a  b 0  1  2   Which seems to be equivalent to   pd DataFrame   a  1  b  2   index  0      a  b 0  1  2

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Pandas magic at work  All logic is out   The error message  ValueError  If using all scalar values  you must pass an index  Says you must pass an index   This does not necessarily mean passing an index makes pandas do what you want it to do  When you pass an index  pandas will treat your dictionary keys as column names and the values as what the column should contain for each of the values in the index   a   2 b   3 df2   pd DataFrame   A  a  B  b   index  1        A   B 1   2   3   Passing a larger index   df2   pd DataFrame   A  a  B  b   index  1  2  3  4        A   B 1   2   3 2   2   3 3   2   3 4   2   3   An index is usually automatically generated by a dataframe when none is given  However  pandas does not know how many rows of 2 and 3 you want  You can however be more explicit about it  df2   pd DataFrame   A   a  4  B   b  4   df2      A   B 0   2   3 1   2   3 2   2   3 3   2   3   The default index is 0 based though   I would recommend always passing a dictionary of lists to the dataframe constructor when creating dataframes  It s easier to read for other developers  Pandas has a lot of caveats  don t make other developers have to experts in all of them in order to read your code

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Another option is to convert the scalars into list on the fly using Dictionary Comprehension  df   pd DataFrame data  k   v  for k  v in mydict items      The expression       creates a new dict whose values is a list of 1 element  such as   In  20   mydict Out 20     a   1   b   2   In  21   mydict2     k   v  for k  v in mydict items     In  22   mydict2 Out 22     a    1    b    2

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You could try this  df2   pd DataFrame from dict   a  a  b  b   orient    index

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The error message says that if you re passing scalar values  you have to pass an index   So you can either not use scalar values for the columns -- e g  use a list    gt  gt  gt  df   pd DataFrame   A    a    B    b     gt  gt  gt  df    A  B 0  2  3   or use scalar values and pass an index    gt  gt  gt  df   pd DataFrame   A   a   B   b   index  0    gt  gt  gt  df    A  B 0  2  3

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If you have a dictionary you can turn it into a pandas data frame with the following line of code    pd DataFrame   key   d keys     value   d values

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You could try   df2   pd DataFrame from dict   a  a  b  b   orient    index     From the documentation on the  orient  argument  If the keys of the passed dict should be the columns of the resulting DataFrame  pass    columns     default   Otherwise if the keys should be rows  pass    index

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You need to create a pandas series first  The second step is to convert the pandas series to pandas dataframe   import pandas as pd data     a   1   b   2  pd Series data  to frame     You can even provide a column name   pd Series data  to frame  ColumnName

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Change your  a  and  b  values to a list  as follows  a    2  b    3   then execute the same code as follows  df2   pd DataFrame   A  a  B  b   df2  and you ll get      A   B 0   2   3

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You need to provide iterables as the values for the Pandas DataFrame columns   df2   pd DataFrame   A   a   B   b

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simplest options ls   dict      A  a  B  b  df   pd DataFrame dict  index   np arange 1

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This is because a DataFrame has two intuitive dimensions - the columns and the rows    You are only specifying the columns using the dictionary keys   If you only want to specify one dimensional data  use a Series

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Maybe Series would provide all the functions you need   pd Series   A  a  B  b     DataFrame can be thought of as a collection of Series hence you can     Concatenate multiple Series into one data frame  as described here   Add a Series variable into existing data frame   example here

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Just pass the dict on a list   a   2 b   3 df2   pd DataFrame    A  a  B  b

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I usually use the following to to quickly create a small table from dicts  Let s say you have a dict where the keys are filenames and the values their corresponding filesizes  you could use the following code to put it into a DataFrame  notice the  items   call on the dict   files     A txt  12   B txt  34   C txt  56   D txt  78  filesFrame   pd DataFrame files items    columns   filename   size    print filesFrame     filename  size 0    A txt    12 1    B txt    34 2    C txt    56 3    D txt    78

[python] Constructing pandas DataFrame from values in variables gives "ValueError: If using all scalar values, you must pass an index"

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