如何使用python ggplot绘制直方图？

Question

I would like to plot an histogram representing the value TP on the y axis and the method on the x axis. In particular I would like to obtain different figures according to the value of the column 'data'.

In this case I want a first histogram with values 2,1,6,9,8,1,0 and a second histogram with values 10,10,16,...

The python version of ggplot seems to be slightly different by the R ones.

            FN FP  TN  TP                   data  method
method                                              
SS0208  18  0  80   2  A p=100 n=100 SNR=0.5  SS0208
SS0408  19  0  80   1  A p=100 n=100 SNR=0.5  SS0408
SS0206  14  9  71   6  A p=100 n=100 SNR=0.5  SS0206
SS0406  11  6  74   9  A p=100 n=100 SNR=0.5  SS0406
SS0506  12  6  74   8  A p=100 n=100 SNR=0.5  SS0506
SS0508  19  0  80   1  A p=100 n=100 SNR=0.5  SS0508
LKSC    20  0  80   0  A p=100 n=100 SNR=0.5    LKSC
SS0208  10  1  79  10   A p=100 n=100 SNR=10  SS0208
SS0408  10  0  80  10   A p=100 n=100 SNR=10  SS0408
SS0206   4  5  75  16   A p=100 n=100 SNR=10  SS0206

As a first step I have tried to plot only one histogram and I received an error.

 df = df[df.data == df.data.unique()[0]]

In [65]: ggplot() + geom_bar(df, aes(x='method', y='TP'), stat='identity')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-65-dd47b8d85375> in <module>()
----> 1 ggplot() + geom_bar(df, aes(x='method', y='TP'), stat='identity')

TypeError: __init__() missing 2 required positional arguments: 'aesthetics' and 'data'w

In [66]: 

I have tried different combinations of commands but I did not solve.

Once that this first problem has been solved I would like the histograms grouped according to the value of 'data'. This could probably be done by 'facet_wrap'

Answer 1

This is probably because you called ggplot() without an argument (Not sure if that should be possible. If you think so, please add a issue on http://github.com/yhat/ggplot ).

Anyway, this should work:

ggplot(df, aes(x='method', y='TP')) + geom_bar(stat='identity')

Unfortunately, faceting with geom_bar doesn't work yet properly (only when all facets have all levels/ x values!) -> Bugreport