I understand that the csv module exists, however for my current project we are not allowed to use the module to call csv files.
My code is as follows;
table = []
for line in open("data.csv"):
data = line.split(",")
table.append(data)
transposed = [[table[j][i] for j in range(len(table))] for i in range(len(table[0]))]
rows = transposed[1][1:]
rows = [float(i) for i in rows]
I'm really new to python so this is probably a massively basic question, I've been scouring the internet all day and struggle to find a solution. All I need to do is to be able to call data from any individual column so I can analyse it. Thanks
your data is organized in a list of lists. Each sub list represents a row. To better illustrate this I would avoid using list comprehensions because they are more difficult to read. Additionally I would avoid using variables like 'i' and 'j' and instead use more descriptive names like row or column. Here is a simple example of how I would accomplish this
def read_csv():
table = []
with open("data.csv") as fileobj:
for line in fileobj.readlines():
data = line.strip().split(',')
table.append(data)
return table
def get_column_data(data, column_index):
column_data = []
for row in data:
cell_data = row[column_index]
column_data.append(cell_data)
return column_data
data = read_csv()
get_column_data(data, column_index=2) #example usage
I'm reading values from an excel workbook and I'm trying to stop printing when the value of a specific cell equals a string. Here is my code
import openpyxl
wb = openpyxl.load_workbook('data.xlsx')
for sheet in wb.worksheets:
nrows = sheet.max_row
ncolumns = sheet.max_column
for rowNum in range(20,sheet.max_row):
Sub = sheet.cell(row=rowNum, column=3).value
Unit = sheet.cell(row=rowNum, column=6).value
Concentration = sheet.cell(row=rowNum, column=9).value
com = rowNum[3]
if Sub == "User:":
pass
else:
print(Sub, Concentration, Unit)
The problem is that the if statement doesn't work. When I use type(Sub), python return <type 'unicode'>
Do you have any idea how to do it ?
Thanks
Sounds like you're test is failing. All strings in Excel files are returned as unicode objects but "User:" == u"User:". Maybe the cells you are looking at have some whitespace that isn't visible in your debug statement. In this case it's useful to embed the string in a list when printing it print([Sub])
Alternatively, and this looks to be the case, you are getting confused between Excel's 1-based indexing and Python's zero based indexing. In you code the first cell to be looked at will be C20 (ws.cell(20, 3)) but rowNum[3] is actually D20.
I also recommend you try and avoid using Python's range and the max_column and max_row properties unless you really need them. In your case, ws.get_squared_range() make more sense. Or, in openpyxl 2.4, which allows specify the known edges of a range of cells.
for row in get_squared_range(ws.min_colum, 20, ws.max_column, ws.max_row):
Sub = row[2].value # 3rd item
Unit = row[5].value
Concentration = row[8].value
In openpyxl 2.4 get_squared_range can be replaced:
for row in ws.iter_rows(min_row=20):
I'm trying to determine "best practice" to do the following without incurring a SettingWithCopyWarning. I'm using python 2.7 and pandas 15.2
What I want to do is subselect a dataframe and then use this selection as a new dataframe, without risking modification to the original. Here's an example of what I'm doing:
import pandas as pd
def select_blue_cars(df):
"""Returns a new dataframe of blue cars"""
return df[df['color'] == 'blue']
cars = pd.DataFrame({'color': ['blue', 'blue', 'red'], 'make': ['Ford', 'BMW', 'Ford']})
blue_cars = select_blue_cars(cars)
blue_cars['price'] = 10000
The above generates a SettingWithCopyWarning in current pandas but otherwise behaves as I want it to (ie. the cars df has not been modified).
What is the best way to implement select_blue_cars so that the subsequent code doesn't trigger this warning?
Should I be using .copy() everywhere?
return df[df['color'] == 'blue'].copy()
(Aside) What's the performance of copy() like?
Eventually I'd like to chain simple transform functions like select_blue_cars:
blue_fords = select_fords(select_blue_cars(cars))
Edit: Having thought about this a bit more I think that I'm looking for a single transform which selects a copy from the dataframe without explicitly calling .copy(). That way I can write functions to do little transformations on the df and chain them.
Transposition for example df.T gives a new dataframe. There's no need to call .copy().
df2 = df.T
df2 = df.T.copy() # no need
It looks like, in the case of selection, .copy() is required for this pattern.
How you get around the SettingWithCopyWarning depends a bit on how long you plan on keeping the subset around. If you just want to briefly look at the price within a particular colour and then return to the overall dataframe, the suggestions JohnE has given are pretty good. If you actually want to keep the subset around and perform a bunch of separate analyses on it, then what I usually do is subset with .loc and explicitly copy, e.g.:
subset = df.loc[df['condition'] > 5, :].copy()
In your code, this would be:
import pandas as pd
def select_blue_cars(df):
"""Returns a new dataframe of blue cars"""
return df.loc[df['color'] == 'blue', :].copy()
cars = pd.DataFrame({'color': ['blue', 'blue', 'red'], 'make': ['Ford', 'BMW', 'Ford']})
blue_cars = select_blue_cars(cars)
blue_cars['price'] = 10000
I think this remains one of the more confusing parts of pandas. You are actually asking 2 or 3 questions and the answers may be less simple than you'd think. Consequently, I'll make the simplifying assumption that you'll just keep everything in one dataset (if not, it's not that big a deal though), and give a simple answer.
What you want to do (in pseudocode):
price = 10000 if color == blue
The simplest way to do this is actually with numpy where():
cars['price'] = np.where( cars['color'] == 'blue', 10000, np.nan )
color make price
0 blue Ford 10000
1 blue BMW 10000
2 red Ford NaN
You can also nest where() so it's really very powerful and simple method for conditional setting like this. You can also use ix/loc/iloc (though you need to create an empty column for 'price' first):
cars.ix[ cars.color == 'blue', 'price' ] = 10000
And to briefly address the chained indexing warning, what it's mostly saying is don't try to do too much on the left hand side when setting values:
df[ df.y > 5 ]['x'] = df['z']
this is OK though:
df['x'] = df[ df.y > 5 ]['z']
Because the result of chained indexing may by a copy rather than reference, which will cause the former to fail but not the latter. You can also get around this by using ix/loc/iloc.
I have a dataframe that contains Physician_Profile_City, Physician_Profile_State and Physician_Profile_Zip_Code. I ultimately want to stratify an analysis based on state, but unfortunately not all of the Physician_Profile_States are filled in. I started looking around to try and figure out how to fill in the missing States. I came across the pyzipcode module which can take as an input a zip code and returns the state as follows:
In [39]: from pyzipcode import ZipCodeDatabase
zcdb = ZipCodeDatabase()
zcdb = ZipCodeDatabase()
zipcode = zcdb[54115]
zipcode.state
Out[39]: u'WI'
What I'm struggling with is how I would iterate through the dataframe and add the appropriate "Physician_Profile_State" when that variable is missing. Any suggestions would be most appreciated.
No need to iterate if the form of the data is a dict then you should be able to perform the following:
df['Physician_Profile_State'] = df['Physician_Profile_Zip_Code'].map(zcdb)
Otherwise you can call apply like so:
df['Physician_Profile_State'] = df['Physician_Profile_Zip_Code'].apply(lambda x: zcdb[x].state)
In the case where the above won't work as it can't generate a Series to align with you df you can apply row-wise passing axis=1 to the df:
df['Physician_Profile_State'] = df[['Physician_Profile_Zip_Code']].apply(lambda x: zcdb[x].state, axis=1)
By using double square brackets we return a df allowing you to pass the axis param
Lets have the following dataframe inside R:
df <- data.frame(sample=rnorm(1,0,1),params=I(list(list(mean=0,sd=1,dist="Normal"))))
df <- rbind(df,data.frame(sample=rgamma(1,5,5),params=I(list(list(shape=5,rate=5,dist="Gamma")))))
df <- rbind(df,data.frame(sample=rbinom(1,7,0.7),params=I(list(list(size=7,prob=0.7,dist="Binomial")))))
df <- rbind(df,data.frame(sample=rnorm(1,2,3),params=I(list(list(mean=2,sd=3,dist="Normal")))))
df <- rbind(df,data.frame(sample=rt(1,3),params=I(list(list(df=3,dist="Student-T")))))
The first column contains a random number of a probability distribution and the second column stores a list with its parameters and name.
The dataframe df looks like:
sample params
1 0.85102972 0, 1, Normal
2 0.67313218 5, 5, Gamma
3 3.00000000 7, 0.7, ....
4 0.08488487 2, 3, Normal
5 0.95025523 3, Student-T
Q1: How can I have the list of name distributions for all records? df$params$dist does not work. For a single record is easy, for example the third one: df$params[[3]]$dist
Q2: Is there any alternative way of storing data like this? something like a multi-dimensional dataframe? I do not want to add columns for each parameter because it will scatter the dataframe with missing values.
It's probably more natural to store information like this in a pure list structure, than in a data frame:
distList <- list(normal = list(sample=rnorm(1,0,1),params=list(mean=0,sd=1,dist="Normal")),
gamma = list(sample=rgamma(1,5,5),params=list(shape=5,rate=5,dist="Gamma")),
binom = list(sample=rbinom(1,7,0.7),params=list(size=7,prob=0.7,dist="Binomial")),
normal2 = list(sample=rnorm(1,2,3),params=list(mean=2,sd=3,dist="Normal")),
tdist = list(sample=rt(1,3),params=list(df=3,dist="Student-T")))
And then if you want to extract just the distribution name from each, we can use sapply to loop over the list and extract just that piece:
sapply(distList,function(x) x[[2]]$dist)
normal gamma binom normal2 tdist
"Normal" "Gamma" "Binomial" "Normal" "Student-T"
If you absolutely must store this information in a data frame, one way of doing so springs to mind. You're currently using a params column in your data frame to store the parameters associated with the distributions. Perhaps a better way of doing this would be to (i) identify the maximum number of parameters that you'll need for any distribution, (ii) store the distribution names in a field called df$distribution, and (iii) store the parameters in dedicated parameter columns, the meaning of which will have to be decided upon based on the type of distribution.
For instance, any row with df$distribution = 'Normal' should have df$param1 = and df$param2 = . A row with df$distribution='Student' should have df$param1 = and df$param2 = NA. Something like the following:
dg <- data.frame(sample=rnorm(1, 0, 1), distribution='Normal',
param1=0, param2=1)
dg <- rbind(dg, data.frame(sample=rgamma(1, 5, 5),
distribution='Gamma', param1=5, param2=5))
dg <- rbind(dg, data.frame(sample=rt(1, 3), distribution='Student',
param1=3, param2=NA))
It's ugly, but it will give you what you want. And don't worry about the missing values; missing values are a fact of life when dealing with non-trivial data frames. They can be dealt with easily in R by appropriate use of things like na.rm and complete.cases().
Based on the data frame you have above,
sapply(df$params,"[[","dist")
(or lapply if you prefer) would work.
I would probably put at least the names of the distributions in their own column, even if you want the parameters to be in variable-length lists.