Python: Multiple conditions questions on pandas columns

Question

I have a question regarding multiple-conditions on pandas columns. I have the following dataframe:

    A   B   C
0   0   9   0
1   1   8   0
2   1   9   0
3   1   5   1
4   1   9   1
5   1   8   1
6   -1  9   0
7   -1  5   -1
8   -1  7   -1

What I am trying to achieve is the following:

1.) If A>0 and B <6 C should become a 1 and keep that until A changes (B could get above 6)

2.) If A<0 and B <6 C should become a -1 and keep that until A changes (B could get above 6)

Any suggestions how to do that without a loop?

I am struggeling with how to "memorize" the status of B having been below 6 for the current A= 1 or A=-1 period.

Thanks for any suggestions

Index B A A>0 & B >0.8 A>0 & as soon as B>0.8 2127 0.551354566 0 0 0 2128 0.66838571 0 0 0 2129 0.809306329 1 1 1 2130 0.812775762 1 1 1 2131 0.81319083 1 1 1 2132 0.814134565 1 1 1 2133 0.814281433 1 1 1 2134 0.812157799 1 1 1 2135 0.810377385 1 1 1 2136 0.808989447 1 1 1 2137 0.806981847 1 1 1 2138 0.800548453 1 1 1 2139 0.792510453 1 0 0 2140 0.785009569 1 0 0 2141 0.777099821 1 0 0 2142 0.768469301 1 0 0 2143 0.762370584 1 0 0 2144 0.754136153 1 0 0 2145 0.74586568 1 0 0 2146 0.74058505 1 0 0 2147 0.733714521 1 0 0 — Rolf12
– Rolf12, Commented Oct 8, 2018 at 16:58

BENY · Accepted Answer · 2018-10-05 16:05:07Z

1

Using np.select create your help column when satisfied your own conditions , then we do groupby with bfill

s1=(df.A>0)&(df.B<6)
s2=(df.A<0)&(df.B<6)
df['v']=np.select([s1,s2],[1,-1])
df.v.replace(0,np.nan).groupby(df.A).ffill().fillna(0).astype(int)
Out[1023]: 
0    0
1    0
2    0
3    1
4    1
5    1
6    0
7   -1
8   -1

edited Oct 5, 2018 at 16:05

answered Oct 5, 2018 at 15:13

BENY

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6 Comments

Karn Kumar Over a year ago

did OP want output to be float rather than int?

BENY Over a year ago

@pygo adding astype(int)

Rolf12 Over a year ago

Many thanks Wen!! Sorry, trying to understand the code. Why would you goupby A and use ffill?

Rolf12 Over a year ago

Unfortunately it seems also not to solve the issue. Here is the concrete example. Index is time.

Rolf12 Over a year ago

Tried to add it but somehow the format is not readable when I copy the table here

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