I have a data frame and want to update specific cells in a column based on a condition on another column.
ID Name Metric Unit Value
2 1 K2 M1 msecond 1
3 1 K2 M2 NaN 10
4 2 K2 M1 usecond 500
5 2 K2 M2 NaN 8
The condition is, if Unit
string is msecond
, then multiply the corresponding value in Value
column by 1000 and store it in the same place. Considering a constant step for row iteration (two-by-two), the following code is not correct
i = 0
while i < len(df_group):
x = df.iloc[i].at["Unit"]
if x == 'msecond':
df.iloc[i].at["Value"] = df.iloc[i].at["Value"] * 1000
i = 2
However, the output is the same as before modifications. How can I fix that? Also what are the alternatives for better coding instead of that while loop?
CodePudding user response:
A much simpler (and more efficient) form would be to use loc
:
df.loc[df['Unit'] == 'msecond', 'Value'] *= 100
If you consider it essentially to only update a specific step of indexes:
step = 2
start = 0
df.loc[df['Unit'].eq('msecond') & (df.index % step == start), 'Value'] *= 100