My first question here so please bare with me.

I'm trying to feed my neural network with training data read in from an excel file. It works perfectly fine when i have less than 50 rows in the sheet. But when i try with the real excel file containing almost 4.000 rows it suddenly takes forever. Although 4.000 is a lot i'm pretty sure my way of doing it is still very inefficient.

as you can see in the code below i'm using the read_excel over and over again in the loop. I feel like there should be a way to only read the whole column 1 time and then work with it from there.

My goal is to read in 5 rows as the 1st input starting from row 0. then reading 5 rows in again but starting from row 1 and 5 rows again starting from row 3 So it's like a window of 5 rows that is read and then moving the window by 1. The output should allways be the 1 row after the window.

**Example:** if row 1-20 contains numbers 1-20 then:
input1 = [1,2,3,4,5] and output1 = 6
input2 = [2,3,4,5,6] and output2 = 7
input15 = [15,16,17,18,19] and output15 = 20
notice how inputs are lists and outputs are just numbers. So when i append those to the final input & output lists i end up with inputs being a list of lists and out being list of outputs

My code

from pandas import read_excel

# initialize final input & output lists. The contents of the temporary input & output lists
# are gonna be appended to these final lists
training_input = []
training_output = []

# excel relevant info
my_sheet = 'Junaid'
file_name = '../Documents/Junaid1.xlsx'

# initialize counters
loop_count = 0
row_counter = 0

for x in range(25):

    # load the excel file containing inputs & outputs
    # using parameters skiprows, nrows (number of rows) and index col
    df = read_excel(file_name, sheet_name = my_sheet, skiprows=row_counter, nrows=6, index_col=0)

    # initialize temporary input & output lists
    input_temp = []
    output_temp = []

    for y in df.index:
        # append the first 5 rows of the 6 to input list
        if loop_count < 5:
            loop_count += 1
            # append the 6th data to output list

    row_counter += 1
    loop_count = 0

1 Answer 1


Well yes it would be slow because you are opening and closing the file for every iteration of the for loop. A general rule in programming is that if the file is not constantly changing, then only open and read it a single time. Also, there are large sections of your code that can be shaved off if you simply use list comprehension

Here, I have rewritten your code to only open the file and read it once, then it creates the two lists using list comprehension and slicing.

from pandas import read_excel

# excel relevant info
my_sheet = 'Junaid'
file_name = '../Documents/Junaid1.xlsx'

df = read_excel(file_name, sheet_name = my_sheet, index_col=0, header=None)

training_input = [df.index[i:i+5].tolist() for i in range(len(df)-5)]
training_output = [df.index[i].tolist() for i in range(5, len(df))]

Also, there seems to be a bug in your code since the excel file you described in your question does not have a header (i.e. the very first row contains data), thus your code skips the very first row of values. To fix that you should pass the parameter "header=None" to the pandas function to tell it that there is no header index. You can read more about that here.

  • $\begingroup$ Hi A Kareem, thanks for your reply. $\endgroup$
    – Casper
    May 1, 2020 at 11:25
  • $\begingroup$ Did, this work for you? If so, please mark my answer as accepted. $\endgroup$
    – A Kareem
    May 1, 2020 at 11:26
  • $\begingroup$ Sorry, i don't know what went wrong. Yes, i did work, thanks a lot. Execution time is under 1 second even with 5k rows :) Kareem, can i ask u 1 more question. What if i have 2 columns of data. so that 1 input element shouldn't just be "5 rows of column A" but "5 rows of column A + 5 rows from column B" ? $\endgroup$
    – Casper
    May 1, 2020 at 13:12
  • $\begingroup$ Then you can do something like this training_input = [df.iloc[i:i+5, 0].tolist() + df.iloc[i:i+5, 1].tolist() for i in range(len(df)-5)] And make sure to remove the index_col=0 argument from the pandas call to get all columns $\endgroup$
    – A Kareem
    May 1, 2020 at 13:33

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