I am trying to subtract value from a column in a dataframe I am trying to do it like this

for i in range(len(Numbers)-1):
    sub = Numbers.loc[i, 'Stock'] - Numbers.loc[i, 'Sold Number']
    Numbers.loc[i, 'PrepNumber'] = Numbers.loc[i 1, 'Stock'] - sub

but this is not working, I am getting this error

numpy.core._exceptions.UFuncTypeError: ufunc 'subtract' did not contain a loop with signature matching types (dtype('int64'), dtype('<U4')) -> None

Edit:

The data that I have looks something like this:

I would like the output to look something like:

Where PrepNumber (Jan-19) = 1089 - (1255 - 1123)

CodePudding user response：

You can make use of .shift(-1) to get the entry of next row, and format the formula as follows to set up the PrepNumber column:

Numbers['PrepNumber'] = Numbers['Stock'].shift(-1) - (Numbers['Stock'] - Numbers['Sold Number'])

With this one-line code, Pandas has already helped you calculated the results for each row without the need to put the codes in a loop. This is the feature that Pandas provides and you should make good use of it and avoid coding in looping style as far as possible.

Result:

print(Numbers)

     Date  Stock  Sold Number  PrepNumber
0  Jan-19   1255         1123       957.0
1  Feb-19   1089         1051       905.0
2  Mar-19    943         1146      1100.0
3  Apr-19    897          992         NaN

CodePudding user response：

your question is not clear, it'd be great if you could provide sample data and the expected results, or explain what you're trying to do a bit more in your future questions.

but if you're trying to add or substract whole columns from each other, and saving the result in a new column then try using this:

Numbers["PrepNumber"] = Numbers["Stock"] - Numbers["Sold Number"]

Also a tip, using for loops to iterate on the records of a dataframe beats the whole purpose of using pandas, and it should be avoided at all times.